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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19, by infecting cells via the interaction of its spike protein (S) with the primary cell receptor angiotensin-converting enzyme (ACE2). To search for inhibitors of this key step in viral infection, we screened an in-house library of multivalent tryptophan derivatives. Using VSV-S pseudoparticles, we identified compound 2 as a potent entry inhibitor lacking cellular toxicity. Chemical optimization of 2 rendered compounds 63 and 65, which also potently inhibited genuine SARS-CoV-2 cell entry. Thermofluor and microscale thermophoresis studies revealed their binding to S and to its isolated receptor binding domain (RBD), interfering with the interaction with ACE2. High-resolution cryoelectron microscopy structure of S, free or bound to 2, shed light on cell entry inhibition mechanisms by these compounds. Overall, this work identifies and characterizes a new class of SARS-CoV-2 entry inhibitors with clear potential for preventing and/or fighting COVID-19.

The S:A222V point mutation, within the G clade, was characteristic of the 20E (EU1) SARS-CoV-2 variant identified in Spain in early summer 2020. This mutation has since reappeared in the Delta subvariant AY.4.2, raising questions about its specific effect on viral infection. We report combined serological, functional, structural and computational studies characterizing the impact of this mutation. Our results reveal that S:A222V promotes an increased RBD opening and slightly increases ACE2 binding as compared to the parent S:D614G clade. Finally, S:A222V does not reduce sera neutralization capacity, suggesting it does not affect vaccine effectiveness.

Aims: We aim to present data obtained from three patients belonging to three unrelated families with an infantile onset demyelinating neuropathy associated to somatic and neurodevelopmental delay and to describe the underlying genetic changes. Methods: We performed whole-exome sequencing on genomic DNA from the patients and their parents and reviewed the clinical, muscle and nerve data, the serial neurophysiological studies, brain and muscle MRIs, as well as the respiratory chain complex activity in the muscle of the three index patients. Computer modelling was used to characterise the new missense variant detected. Results: All three patients had a short stature, delayed motor milestone acquisition, intellectual disability and cerebellar abnormalities associated with a severe demyelinating neuropathy, with distinct morphological features. Despite the proliferation of giant mitochondria, the mitochondrial respiratory chain complex activity in skeletal muscle was normal, except in one patient in whom there was a mild decrease in complex I enzyme activity. All three patients carried the same two compound heterozygous variants of the TRMT5 (tRNA Methyltransferase 5) gene, one known pathogenic frameshift mutation [c.312_315del (p.Ile105Serfs*4)] and a second rare missense change [c.665 T > C (p.Ile222Thr)]. TRMT5 is a nuclear-encoded protein involved in the post-transcriptional maturation of mitochondrial tRNA. Computer modelling of the human TRMT5 protein structure suggests that the rare p.Ile222Thr mutation could affect the stability of tRNA binding. Conclusions: Our study expands the phenotype of mitochondrial disorders caused by TRTM5 mutations and defines a new form of recessive demyelinating peripheral neuropathy.

Our clinical series comprises 124 patients with movement disorders (MDs) and/or ataxia with cerebellar atrophy (CA), many of them showing signs of neurodegeneration with brain iron accumulation (NBIA). Ten NBIA genes are accepted, although isolated cases compatible with abnormal brain iron deposits are known. The patients were evaluated using standardised clinical assessments of ataxia and MDs. First, NBIA genes were analysed by Sanger sequencing and 59 patients achieved a diagnosis, including the detection of the founder mutation PANK2 p.T528M in Romani people. Then, we used a custom panel MovDisord and/or exome sequencing; 29 cases were solved with a great genetic heterogeneity (34 different mutations in 23 genes). Three patients presented brain iron deposits with Fe-sensitive MRI sequences and mutations in FBXO7, GLB1, and KIF1A, suggesting an NBIA-like phenotype. Eleven patients showed very early-onset ataxia and CA with cortical hyperintensities caused by mutations in ITPR1, KIF1A, SPTBN2, PLA2G6, PMPCA, and PRDX3. The novel variants were investigated by structural modelling, luciferase analysis, transcript/minigenes studies, or immunofluorescence assays. Our findings expand the phenotypes and the genetics of MDs and ataxias with early-onset CA and cortical hyperintensities and highlight that the abnormal brain iron accumulation or early cerebellar gliosis may resembling an NBIA phenotype.

Peroxiredoxin 3 (PRDX3) encodes a mitochondrial antioxidant protein, which is essential for the control of reactive oxygen species homeostasis. So far, PRDX3 mutations are involved in mild-to-moderate progressive juvenile onset cerebellar ataxia. We aimed to unravel the molecular bases underlying the disease in an infant suffering from cerebellar ataxia that started at 19 months old and presented severe cerebellar atrophy and peripheral neuropathy early in the course of disease. By whole exome sequencing, we identified a novel homozygous mutation, PRDX3 p.D163E, which impaired the mitochondrial ROS defense system. In mouse primary cortical neurons, the exogenous expression of PRDX3 p.D163E was reduced and triggered alterations in neurite morphology and in mitochondria. Mitochondrial computational parameters showed that p.D163E led to serious mitochondrial alterations. In transfected HeLa cells expressing the mutation, mitochondria accumulation was detected by correlative light electron microscopy. Mitochondrial morphology showed severe changes, including extremely damaged outer and inner membranes with a notable cristae disorganization. Moreover, spherical structures compatible with lipid droplets were identified, which can be associated with a generalized response to stress and can be involved in the removal of unfolded proteins. In the patient's fibroblasts, PRDX3 expression was nearly absent. The biochemical analysis suggested that the mutation p.D163E would result in an unstable structure tending to form aggregates that trigger unfolded protein responses via mitochondria and endoplasmic reticulum. Altogether, our findings broaden the clinical spectrum of the recently described PRDX3-associated neurodegeneration and provide new insight into the pathological mechanisms underlying this new form of cerebellar ataxia.

Cerebellar atrophy (CA) is a frequent neuroimaging finding in paediatric neurology, usually associated with cerebellar ataxia. The list of genes involved in hereditary forms of CA is continuously growing and reveals its genetic complexity. We investigated ten cases with early-onset cerebellar involvement with and without ataxia by exome sequencing or by a targeted panel with 363 genes involved in ataxia or spastic paraplegia. Novel variants were investigated by in silico or experimental approaches. Seven probands carry causative variants in well-known genes associated with CA or cerebellar hypoplasia: SETX, CACNA1G, CACNA1A, CLN6, CPLANE1, and TBCD. The remaining three cases deserve special attention; they harbour variants in MAST1, PI4KA and CLK2 genes. MAST1 is responsible for an ultrarare condition characterised by global developmental delay and cognitive decline; our index case added ataxia to the list of concomitant associated symptoms. PIK4A is mainly related to hypomyelinating leukodystrophy; our proband presented with pure spastic paraplegia and normal intellectual capacity. Finally, in a patient who suffers from mild ataxia with oculomotor apraxia, the de novo novel CLK2 c.1120T>C variant was found. The protein expression of the mutated protein was reduced, which may indicate instability that would affect its kinase activity.

[Background] The SARS-CoV-2 spike protein (S) mediates the interaction of the virus with cellular membrane receptor (angiotensin-converting enzyme 2, ACE2). In previous PTI meetings, we reported heterologous production in vitro of the ACE2 extracellular domains modified by site-directed mutagenesis to increase its affinity for the S protein, to enable it to be used as viral entry inhibitor (decoy) by competing with the membrane-bound cellular receptor. We now test the value of these decoys for: 1) binding to S variants that emerged during the evolution of the pandemic in viral lineages of concern; and 2) inhibiting experimental cellular infection by pseudotyped virus expressing these S variants. Cellular syncytia formation has been described in several organs as a manifestation of severe COVID-19, and likely has pathogenic impact. To test further our decoys’ effectiveness, we studied their impact on cellular syncytia formation within an experimental in vitro cell culture model. Searching for effective decoys, we produced monomeric and dimeric ACE2 proteins, depending on the respective absence/presence of the extracellular collectrin domain. Interestingly, there are no reported structures of dimeric soluble ACE2 bound to the S protein. After extensive knowledge-guided trial-and-error, we succeeded in visualizing by cryo-electron microscopy (cryoEM) this interaction (~7-Å-resolution), and in understanding the challenges inherent in determining such a complex structural organization., [Methods] 1) Recombinant production and purification of the monomeric or dimeric ACE2, their decoys the receptor binding domain (RBD) and the S protein variants of interest. We used baculovirus/insect cells to produce ACE2s and RBDs, and human Expi293F cells for the S proteins. 2) Biolayer interferometry for assessing protein-protein interactions; 3) Use of a model system for monitoring viral cellular infection and its inhibition by decoys. We used a pseudotyped engineered vesicular stomatitis virus expressing and exposing at its surface the desired S protein variant, to infect appropriate SARS-CoV-2-susceptible mammalian cells; 4) Single-particle cryoEM; 5) Syncytia formation testing using an engineered cultured cell system in which heterologous surface expression of the S protein in one cell type induces syncytium formation in other cells expressing membrane-bound ACE2., [Results] Our decoys proved highly effective in preventing cellular infection by pseudotyped virus expressing the S proteins of different SARS-CoV-2 variants of concern. Biophysical results have validated the maintained interaction between the decoy and the various S protein variants. When introduced into the cellular model system for syncytia formation, the decoys proved capable of decreasing such formation. Puzzlingly, the monomeric decoy was more effective than the dimeric one. The cryoEM images unveiled an ACE2 dimer configuration, where the subunits, resembling the previously reported monomer, were oriented at an angle of >60º, in which the vortex was the interlinked collectrin domains. Both catalytic domains engage with a single RBD of one subunit from different S trimers. The formation of a network at high stoichiometries of both components poses a challenge for structure determination by cryoEM., [Conclusions] Unlike therapeutic antibodies, which proved ineffective on variants not initially used for their production, our decoys should be effective in preventing infection by all widely widespread SARS-CoV-2 variants.

El virus SARS-CoV-2 causa el COVID-19 al infectar las células a través de la interacción de la proteína de su espícula (S) con el receptor celular enzima convertidora de angiotensina 2 (ACE2). Para buscar inhibidores de este paso clave en la infección viral, examinamos una biblioteca interna (IQM-CSIC, Madrid) de compuestos multivalentes derivados de triptófano, primero usando pseudopartículas de Virus de Estomatits Vesicular que expresaban S (I2SysBio, UV y CSIC, Valencia), identificando un compuesto como potente inhibidor de entrada no citotóxico. La optimización química (IQM-CSIC) generó otros dos potentes inhibidores de entrada no citotóxicos que, como 2, también inhibieron la entrada celular de SARS-CoV-2 genuino (I2SysBio). Los estudios con proteínas recombinantes puras (IBV-CSIC, Valencia) usando termofluor y termoforesis de microescala revelaron la unión de estos compuestos a S, y a su dominio de unión al receptor producido separadamente, probando interferencia con la interacción con ACE2. La criomicroscopía electrónica de S (IBV-CSIC), libre o unido al compuesto activo, arrojó luz sobre los mecanismos de inhibición por estos compuestos de la entrada viral a la célula. Esta actividad triinstitucional combinada ha identificado y caracterizado una nueva clase de inhibidores de entrada de SARS-CoV-2 de claro potencial preventivo o terapéutico de COVID-19.

The S:A222V point mutation, within the G clade, was characteristic of the 20E (EU1) SARS-CoV-2 variant identified in Spain in early summer 2020. This mutation has now reappeared in the Delta subvariant AY.4.2, raising questions about its specific effect on viral infection. We report combined serological, functional, structural and computational studies characterizing the impact of this mutation. Our results reveal that S:A222V promotes an increased RBD opening and slightly increases ACE2 binding as compared to the parent S:D614G clade. Finally, S:A222V does not reduce sera neutralization capacity, suggesting it does not affect vaccine effectiveness.

Our clinical series comprises 124 patients with movement disorders (MDs) and/or ataxia with cerebellar atrophy (CA), many of them showing signs of neurodegeneration with brain iron accumulation (NBIA). Ten NBIA genes are accepted, although isolated cases compatible with abnormal brain iron deposits are known. The patients were evaluated using standardised clinical assessments of ataxia and MDs. First, NBIA genes were analysed by Sanger sequencing and 59 patients achieved a diagnosis, including the detection of the founder mutation PANK2 p.T528M in Romani people. Then, we used a custom panel MovDisord and/or exome sequencing; 29 cases were solved with a great genetic heterogeneity (34 different mutations in 23 genes). Three patients presented brain iron deposits with Fe-sensitive MRI sequences and mutations in FBXO7, GLB1, and KIF1A, suggesting an NBIA-like phenotype. Eleven patients showed very early-onset ataxia and CA with cortical hyperintensities caused by mutations in ITPR1, KIF1A, SPTBN2, PLA2G6, PMPCA, and PRDX3. The novel variants were investigated by structural modelling, luciferase analysis, transcript/minigenes studies, or immunofluorescence assays. Our findings expand the phenotypes and the genetics of MDs and ataxias with early-onset CA and cortical hyperintensities and highlight that the abnormal brain iron accumulation or early cerebellar gliosis may resembling an NBIA phenotype.

(Póster 63) Background: Single-particle cryoelectron microscopy (cryoEM) has played a key role in the fight against COVID-19. The molecular mechanisms for the action of some of the currently approved drugs targeting the SARS-CoV-2 RNA-dependent RNA polymerase, the fast developments of the current available vaccines and antibody therapies are examples of the impact of the knowledge gained from the cryoEM structures of SARS-CoV-2 proteins in complex with proteins (ACE2 or antibodies/nanobodies) or small compounds. Our aim is to use this technology to understand structurally how certain antiviral compounds and proteins targeting the spike may inhibit viral entry. Methods: 1) Production of wild-type and mutated spike and ACE2 proteins using baculovirus/insect cells. 2) Spike binding kinetics: protein-protein and protein-small compound interactions measured by BLI Biolayer interferometry (BLI) and/or microscale Thermophoresis (MST). 3) Buffer optimization for cryoEM grid preparation of spike variants by thermal shift assays and negative-staining electron microscopy (NSEM). These techniques are also used to adjust the molar ratio of spike:ACE2 and spike:small-compound complexes. 4) Structural characterization by cryoEM. Results: At IBV-CSIC we have created a pipeline for the production and characterization of several spike variants and ACE2 decoys. While this pipeline is described in detail in other oral/poster communications, this communication is centered around one of the pillars within this pipeline; the structural characterization of possible drug candidates bound to the SARS-CoV-2 spike by cryoEM. In this way, we have successfully solved structures of the spike bound to: A) protein inhibitors as ACE2 decoys; B) a small inhibitory compound; C) mixtures of proteins and small-compound (nanobody-heparan derivative) working cooperatively as inhibitors. These protein/drug candidates were previously selected based on the results obtained in our interactomics platform, wher

CIBER (Center for Biomedical Network Research; Centro de Investigación Biomédica En Red) is a public national consortium created in 2006 under the umbrella of the Spanish National Institute of Health Carlos III (ISCIII). This innovative research structure comprises 11 different specific areas dedicated to the main public health priorities in the National Health System. CIBERER, the thematic area of CIBER focused on rare diseases (RDs) currently consists of 75 research groups belonging to universities, research centers, and hospitals of the entire country. CIBERER's mission is to be a center prioritizing and favoring collaboration and cooperation between biomedical and clinical research groups, with special emphasis on the aspects of genetic, molecular, biochemical, and cellular research of RDs. This research is the basis for providing new tools for the diagnosis and therapy of low-prevalence diseases, in line with the International Rare Diseases Research Consortium (IRDiRC) objectives, thus favoring translational research between the scientific environment of the laboratory and the clinical setting of health centers. In this article, we intend to review CIBERER's 15-year journey and summarize the main results obtained in terms of internationalization, scientific production, contributions toward the discovery of new therapies and novel genes associated to diseases, cooperation with patients' associations and many other topics related to RD research.

(G01 35 P 027) La CPS1 es la entrada-interruptor del ciclo de la urea, operada por su activador esencial N-acetil-L-glutamato (NAG). Este ciclo es clave para la detoxificación del amonio derivado del catabolismo de las proteínas. Nuestras dos estructuras cristalinas de CPS1 humana sin ligandos o unidas a 2ADP, K+, Mg2+ y NAG, demostraron (De Cima et al. Sci Reports2015) su composición por 6 dominios globulares, dos de ellos catalíticos y homólogos, otro de activación por NAG y un cuarto de integración, quedando por determinar la función de sus dos dominios N-terminales (~400 aas.), reminiscentes de la subunidad menor de las CPSs anabólicas bacterianas. Hemos abordado la determinación de dicha función mediante mutagénesis dirigida, usando los datos genéticos de pacientes con déficit de CPS1 como atajo para elegir qué mutaciones introducir. En 30 mutantes humanos de estos dominios, producidos en y purificados de un sistema de baculovirus/células de insecto, hemos realizado ensayos de estabilidad, de actividad enzimática, y determinado las constantes cinéticas para los sustratos y el NAG. Los resultados indican un importante papel estabilizador de los dominios N-terminales, explicando su conservación en CPS1 a pesar de que han perdido la función ancestral glutaminasa de la subunidad menor de las CPSs bacterianas. Las estructuras ya determinadas, representativas de ambos extremos del proceso de activación de la CPS1, junto con una nueva estructura presentada aquí para una forma intermedia de activación pre-unión de NAG, fundamentan estructuralmente dicho papel estabilizador, a la vez que arrojan luz sobre el inicio del proceso de activación.

The PII‐like protein CutA is annotated as being involved in Cu2+ tolerance, based on analysis of Escherichia coli mutants. However, the precise cellular function of CutA remains unclear. Our bioinformatic analysis reveals that CutA proteins are universally distributed across all domains of life. Based on sequence‐based clustering, we chose representative cyanobacterial CutA proteins for physiological, biochemical, and structural characterization and examined their involvement in heavy metal tolerance, by generating CutA mutants in filamentous Nostoc sp. and in unicellular Synechococcus elongatus. However, we were unable to find any involvement of cyanobacterial CutA in metal tolerance under various conditions. This prompted us to re‐examine experimentally the role of CutA in protecting E. coli from Cu2+. Since we found no effect on copper tolerance, we conclude that CutA plays a different role that is not involved in metal protection. We resolved high‐resolution CutA structures from Nostoc and S. elongatus. Similarly to their counterpart from E. coli and to canonical PII proteins, cyanobacterial CutA proteins are trimeric in solution and in crystal structure; however, no binding affinity for small signaling molecules or for Cu2+ could be detected. The clefts between the CutA subunits, corresponding to the binding pockets of PII proteins, are formed by conserved aromatic and charged residues, suggesting a conserved binding/signaling function for CutA. In fact, we find binding of organic Bis‐Tris/MES molecules in CutA crystal structures, revealing a strong tendency of these pockets to accommodate cargo. This highlights the need to search for the potential physiological ligands and for their signaling functions upon binding to CutA.

he PII-like protein CutA is annotated as being involved in Cu2+ tolerance, based on analysis of Escherichia coli mutants. However, the precise cellular function of CutA remains unclear. Our bioinformatic analysis reveals that CutA proteins are universally distributed across all domains of life. Based on sequence-based clustering, we chose representative cyanobacterial CutA proteins for physiological, biochemical, and structural characterization and examined their involvement in heavy metal tolerance, by generating CutA mutants in filamentous Nostoc sp. and in unicellular Synechococcus elongatus. However, we were unable to find any involvement of cyanobacterial CutA in metal tolerance under various conditions. This prompted us to re-examine experimentally the role of CutA in protecting E. coli from Cu2+ . Since we found no effect on copper tolerance, we conclude that CutA plays a different role that is not involved in metal protection. We resolved high-resolution CutA structures from Nostoc and S. elongatus. Similarly to their counterpart from E. coli and to canonical PII proteins, cyanobacterial CutA proteins are trimeric in solution and in crystal structure; however, no binding affinity for small signaling molecules or for Cu2+ could be detected. The clefts between the CutA subunits, corresponding to the binding pockets of PII proteins, are formed by conserved aromatic and charged residues, suggesting a conserved binding/signaling function for CutA. In fact, we find binding of organic Bis-Tris/MES molecules in CutA crystal structures, revealing a strong tendency of these pockets to accommodate cargo. This highlights the need to search for the potential physiological ligands and for their signaling functions upon binding to CutA. DATABASES: Structural data are available in Protein Data Bank (PDB) under the accession numbers 6GDU, 6GDV, 6GDW, 6GDX, 6T76, and 6T7E.

PII, a homotrimeric very ancient and highly widespread (bacteria, archaea, plants) key sensor-transducer protein, conveys signals of abundance or poorness of carbon, energy and usable nitrogen, converting these signals into changes in the activities of channels, enzymes, or of gene expression. PII sensing is mediated by the PII allosteric effectors ATP, ADP (and, in some organisms, AMP), 2-oxoglutarate (2OG; it reflects carbon abundance and nitrogen scarcity) and, in many plants, L-glutamine. Cyanobacteria have been crucial for clarification of the structural bases of PII function and regulation. They are the subject of this review because the information gathered on them provides an overall structure-based view of a PII regulatory network. Studies on these organisms yielded a first structure of a PII complex with an enzyme, (N-acetyl-Lglutamate kinase, NAGK), deciphering how PII can cause enzyme activation, and how it promotes nitrogen stockpiling as arginine in cyanobacteria and plants. They have also revealed the first clear-cut mechanism by which PII can control gene expression. A small adaptor protein, PipX, is sequestered by PII when nitrogen is abundant and is released when is scarce, swapping partner by binding to the 2OG-activated transcriptional regulator NtcA, co-activating it. The structures of PII-NAGK, PII-PipX, PipX alone, of NtcA in inactive and 2OG-activated forms and as NtcA-2OG-PipX complex, explain structurally PII regulatory functions and reveal the changing shapes and interactions of the T-loops of PII depending on the partner and on the allosteric effectors bound to PII. Cyanobacterial studies have also revealed that in the PII-PipX complex PipX binds an additional transcriptional factor, PlmA, thus possibly expanding PipX roles beyond NtcA-dependency. Further exploration of these roles has revealed a functional interaction of PipX with PipY, a pyridoxal-phosphate (PLP) protein involved in PLP homeostasis whose mutations in the human ortholog

The paper 'Interaction of N-acetyl-l-glutamate kinase with the PII signal transducer in the non-photosynthetic alga Polytomella parva: Co-evolution towards a hetero-oligomeric enzyme' by Selim et al. highlights how the study of a true taxonomic oddity, the heterotrophic unicellular alga P. parva, has been instrumental in uncovering the large potential for adaptive variation in the signaling complex of PII with the enzyme N-acetylglutamate kinase (NAGK). This complex modifies the regulatory properties of NAGK, allowing nitrogen stockpiling as arginine. In P. parva, a stable PII-NAGK complex is formed which lacks regulation by canonical PII effectors but which exhibits novel adaptive responses to nitrogen abundance mediated by glutamine, a neo-effector of PII proteins of photosynthetic eukaryotes.

In two siblings, who suffer from an early childhood-onset axonal polyneuropathy with exclusive involvement of motor fibers, the c.629T>C (p.F210S) mutation was identified in the X-linked AIFM1 gene, which encodes for the apoptosis-inducing factor (AIF). The mutation was predicted as deleterious, according to in silico analysis. A decreased expression of the AIF protein, altered cellular morphology, and a fragmented mitochondrial network were observed in the proband's fibroblasts. This new form of motor neuropathy expands the phenotypic spectrum of AIFM1 mutations and therefore, the AIFM1 gene should be considered in the diagnosis of hereditary motor neuropathies.

[ES] La N-acetil-L-glutamato sintasa (NAGS) es un enzima mitocondrial que cataliza la acetilación de L-glutamato utilizando acetil coenzima A, produciendo N-acetil-L-glutamato (NAG), activador esencial del primer enzima del ciclo de la urea, la carbamoil fosfato sintetasa I. El ciclo de la urea es la ruta metabólica que convierte el amonio producido en el catabolismo proteico en urea. Mientras que el amonio es una sustancia tóxica la urea es una molécula inocua que se excreta en la orina. El déficit de N-acetil-L-glutamato sintasa (NAGSD; OMIM #237310) es causado por mutaciones en el gen NAGS (17q21.31). Es el desorden más raro del ciclo de la urea, siendo indistinguible clínicamente del déficit de carbamoil fosfato sintetasa I (CPSID). Existen formas muy severas de NAGSD, que se presentan en el periodo neonatal temprano, y formas menos severas de aparición más tardía. Los síntomas incluyen vómitos recurrentes, alteraciones neurológicas como letargia y convulsiones, con progresión a coma e incluso a la muerte. Puesto que NAGSD y CPSID son clínicamente indistinguibles, su diagnóstico diferencial se basa en la práctica hoy en la identificación de mutaciones en el gen correspondiente. Este diagnóstico diferencial es clave, ya que solo la NAGSD tiene tratamiento sustitutivo eficaz, la administración de N-carbamil-L-glutamato (NCG; denominación farmacéutica, ácido carglúmico), un medicamento huérfano análogo del NAG que es absorbible por vía oral y es resistente a las deacilasas tisulares, y que activa a la CPSI, reemplazando al acetilglutamato. Para establecer correlaciones genotipo-fenotipo es clave producir NAGS de manera recombinante introduciendo a voluntad las mutaciones identificadas en pacientes y estudiar experimentalmente los efectos de estas mutaciones sobre la estabilidad y la funcionalidad de la NAGS. Al no disponer de un sistema que permitiera la producción recombinante y purificación de NAGS humana, enzima muy inestable, el laboratorio del Dr. Rubio usó co, [EN] N-acetyl-L-glutamate synthase (NAGS) is a mitochondrial enzyme that catalyzes the acetylation of L-glutamate using acetyl coenzyme A, producing N-acetyl-L-glutamate (NAG), an essential activator of the first enzyme in the cycle of the urea, carbamoyl phosphate synthetase I. The urea cycle is the metabolic pathway that converts the ammonium produced in protein catabolism into urea. While ammonium is a toxic substance, urea is a harmless molecule that is excreted in the urine. The N-acetyl-L-glutamate synthase deficiency (NAGSD; OMIM # 237310) is caused by mutations in the NAGS gene (17q21.31). It is the rarest disorder of the urea cycle, being clinically indistinguishable from carbamoyl phosphate synthetase I (CPSID) deficiency. There are very severe forms of NAGSD, which occur in the early neonatal period, and less severe forms of later onset. Symptoms include recurrent vomiting, neurological disorders such as lethargy and seizures, with progression to coma and even death. Since NAGSD and CPSID are clinically indistinguishable, their differential diagnosis is based on practice today in the identification of mutations in the corresponding gene. This differential diagnosis is key, since only NAGSD has effective replacement therapy, the administration of N-carbamil-L-glutamate (NCG; pharmaceutical name, carglumic acid), an orphaned NAG analogue drug that is orally absorbable and is resistant to tissue deacylases, and that activates CPSI, replacing acetylglutamate. To establish genotype-phenotype correlations, it is essential to produce NAGS recombinantly by introducing the mutations identified in patients at will and to study experimentally the effects of these mutations on the stability and functionality of NAGS. Not having a system that allowed the recombinant production and purification of human NAGS, a very unstable enzyme, Dr. Rubio's laboratory used as a model a bacterial NAGS, of Pseudomona aeruginosa, in which he introduced some of the clinical mutations d

[ES] La ornitina transcarbamilasa (OTC) es un enzima mitocondrial que cataliza el segundo paso del ciclo de la urea, la reacción entre carbamil fosfato y ornitina para formar citrulina y fosfato. Esta ruta metabólica convierte el amonio derivado del catabolismo proteico, que es altamente tóxico, en urea, molécula inocua que se elimina en la orina. [1] Mutaciones en el gen para OTC (Xp21.1) causan la deficiencia de OTC (OTCD), el error más frecuente del ciclo de la urea. Los síntomas de OTCD se deben a la toxicidad del amonio acumulado y son variables dependiendo de la mutación presente en hemicigosis en los pacientes. Su forma más severa, neonatal temprana, generalmente afecta a varones, manifestándose con irritabilidad, falta de energía y apetito, letargia, convulsiones y coma. Aunque tratable, la OTCD puede conducir a la muerte o al retraso del desarrollo, discapacidad intelectual y daño hepático. Con menos frecuencia, la OTCD se manifiesta tardíamente, generalmente en presentaciones menos graves, tanto en hombres como en mujeres. Sus síntomas pueden incluir episodios de delirio, nivel reducido de conciencia, dolores de cabeza, vómitos, convulsiones y pérdidas prolongadas de conciencia en situaciones de estrés catabólico (parto, accidentes, cirugía, etc). [1] Para entender el funcionamiento de la OTC, establecer correlaciones genotipo-fenotipo y determinar el impacto de las mutaciones descritas (la mayoría de ellas sustituciones de aminoácido [2]) sobre la estabilidad, la actividad y los parámetros cinéticos, es clave producir OTC humana recombinante. En el laboratorio esto se consigue utilizando un sistema de expresión en E. coli [3] en el que la forma madura de OTC humana (es decir, sin secuencia señal de internalización mitocondrial) se coexpresa en presencia de chaperonas sobreexpresadas que favorecen su correcto plegamiento [3]. El procedimiento de purificación empleado (modificado de [4]) es laborioso, implica cinco etapas de purificación, incluyendo precipi, [EN] Ornithine transcarbamylase (OTC) is a mitochondrial enzyme that catalyzes the second step of the urea cycle, the reaction between carbamyl phosphate and ornithine to form citrulline and phosphate. This metabolic pathway converts ammonium derived from protein catabolism, which is highly toxic, into urea, an innocuous molecule that is eliminated in the urine. [1] Mutations in the gene for OTC (Xp21.1) cause OTC deficiency (OTCD), the most frequent error of the urea cycle. The symptoms of OTCD are due to the toxicity of the accumulated ammonium and are variable depending on the mutation present in hemizigosis in patients. It s more severe, early neonatal form usually affects males, festering with irritability, lack of energy and appetite, lethargy, seizures and coma. Although treatable, OTCD can lead to death or developmental delay, intellectual disability and liver damage. Less frequently, OTCD manifests itself late, usually in less severe presentations, in both men and women. Its symptoms may include episodes of delirium, reduced level of consciousness, headaches, vomiting, seizures and prolonged loss of consciousness in situations of catabolic stress (childbirth, accidents, surgery, etc). [1] To understand the functioning of OTC, establish genotype-phenotype correlations and determine the impact of the described mutations (most of them amino acid substitutions [2]) on stability, activity and kinetic parameters, it is key to produce recombinant human OTC . In the laboratory this is achieved using an expression system in E. coli [3] in which the mature form of human OTC (ie, without a mitochondrial internalization signal sequence) is co-expressed in the presence of overexpressed chaperones that favor its correct folding [3]. The purification procedure employed (modified from [4]) is laborious, involving five purification steps, including ammonium sulfate precipitation, dialysis and ion exchange chromatography. Affinity purification using as ligand N-5-phosphonace

PII, a homotrimeric very ancient and highly widespread (bacteria, archaea, plants) key sensor-transducer protein, conveys signals of abundance or poorness of carbon, energy and usable nitrogen, converting these signals into changes in the activities of channels, enzymes, or of gene expression. PII sensing is mediated by the PII allosteric effectors ATP, ADP (and, in some organisms, AMP), 2-oxoglutarate (2OG; it reflects carbon abundance and nitrogen scarcity) and, in many plants, L-glutamine. Cyanobacteria have been crucial for clarification of the structural bases of PII function and regulation. They are the subject of this review because the information gathered on them provides an overall structure-based view of a PII regulatory network. Studies on these organisms yielded a first structure of a PII complex with an enzyme, (N-acetyl-Lglutamate kinase, NAGK), deciphering how PII can cause enzyme activation, and how it promotes nitrogen stockpiling as arginine in cyanobacteria and plants. They have also revealed the first clear-cut mechanism by which PII can control gene expression. A small adaptor protein, PipX, is sequestered by PII when nitrogen is abundant and is released when is scarce, swapping partner by binding to the 2OG-activated transcriptional regulator NtcA, co-activating it. The structures of PII-NAGK, PII-PipX, PipX alone, of NtcA in inactive and 2OG-activated forms and as NtcA-2OG-PipX complex, explain structurally PII regulatory functions and reveal the changing shapes and interactions of the T-loops of PII depending on the partner and on the allosteric effectors bound to PII. Cyanobacterial studies have also revealed that in the PII-PipX complex PipX binds an additional transcriptional factor, PlmA, thus possibly expanding PipX roles beyond NtcA-dependency. Further exploration of these roles has revealed a functional interaction of PipX with PipY, a pyridoxal-phosphate (PLP) protein involved in PLP homeostasis whose mutations in the human ortholog