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Despite sharing conserved substrate-binding residues, members of 3-hydroxyisobutyrate dehydrogenase (HIBADH) superfamily show remarkable differences in substrate preference. Cysteine residues were identified within a radius of 6 Å surrounding both the active site and the substrate entry site of HIBADH enzyme from Mycobacterium tuberculosis (MtHIBADH). Chemical modification with thiol-modifying reagents, pCMB and DTNB, abrogated the dehydrogenase activity of the enzyme. The loss in activity followed pseudofirst-order kinetics as a function of the concentration of pCMB. S-HIBA (substrate) binding provided partial protection, while NAD (cofactor) binding provided ~70% protection from thiol-modifying reagent. Site-directed mutagenesis of cysteine residues present in the MtHIBADH enzyme identified the indispensable role of Cys-210 residue, located at C-terminal domain, for its dehydrogenase activity. Cys-210 mutation to serine reduced the dehydrogenase activity by ~2-fold while mutation to alanine strikingly reduced the activity by ~140-fold. C210A mutation did not perturb the state of oligomerization of the enzyme but perturbed the secondary structure content. Structural analysis revealed the involvement of Cys-210 residue in inter-chain interaction with Gln178, which acts as hydrogen bond donor and coordinates with Cys-210 and Gly-208 of the adjacent subunit. The data demonstrate a critical role of Cys210 residue in maintaining the conformation and rigidity of loop composed of substrate-interacting residues involved in the entry of S-HIBA substrate in MtHIBADH. [ABSTRACT FROM AUTHOR]

The neurological phenotype of 3‐hydroxyisobutyryl‐CoA hydrolase (HIBCH) and short‐chain enoyl‐CoA hydratase (SCEH) defects is expanding and natural history studies are necessary to improve clinical management. From 42 patients with Leigh syndrome studied by massive parallel sequencing, we identified five patients with SCEH and HIBCH deficiency. Fourteen additional patients were recruited through collaborations with other centres. In total, we analysed the neurological features and mutation spectrum in 19 new SCEH/HIBCH patients. For natural history studies and phenotype to genotype associations we also included 70 previously reported patients. The 19 newly identified cases presented with Leigh syndrome (SCEH, n = 11; HIBCH, n = 6) and paroxysmal dystonia (SCEH, n = 2). Basal ganglia lesions (18 patients) were associated with small cysts in the putamen/pallidum in half of the cases, a characteristic hallmark for diagnosis. Eighteen pathogenic variants were identified, 11 were novel. Among all 89 cases, we observed a longer survival in HIBCH compared to SCEH patients, and in HIBCH patients carrying homozygous mutations on the protein surface compared to those with variants inside/near the catalytic region. The SCEH p.(Ala173Val) change was associated with a milder form of paroxysmal dystonia triggered by increased energy demands. In a child harbouring SCEH p.(Ala173Val) and the novel p.(Leu123Phe) change, an 83.6% reduction of the protein was observed in fibroblasts. The SCEH and HIBCH defects in the catabolic valine pathway were a frequent cause of Leigh syndrome in our cohort. We identified phenotype and genotype associations that may help predict outcome and improve clinical management. [ABSTRACT FROM AUTHOR]

Abstract Members of the Acyl-CoA dehydrogenase (ACADs) family of enzymes play a crucial role in cholesterol and steroid catabolism and are widely studied in the oldest known human pathogen, Mycobacterium tuberculosis (Mtb). However, there is a paucity of information on ACADs involved in branched chain amino acid catabolism. Here we characterized one of the putative ACAD enzyme, fad E9, as "Isobutyryl CoA Dehydrogenase (IBDH)" using a combined computational and experimental approach, guided by homology modeled structural information, affirming its role in valine catabolism. Multiple sequence alignment and phylogenetic analysis place it in a separate cluster from a recently identified family of α2β2 -heterotetramer ACADs in Mtb , based on the position of the conserved Arg247 and catalytic Glu368 residues. The conserved Arg247 was predicted to play an essential role at the center of H-bonding network of reaction center and was confirmed by the reduced activity of R247K mutant. Thus, in addition to the finding of an architecturally distinct α2β2 -heterotetramer among ACADs, these studies also highlight the differences between Mt IBDH, fad E9 from the other ACADs that are involved in cholesterol and steroid catabolism of Mtb. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Isobutyryl-CoA dehydrogenase deficiency (IBDHD) is a rare autosomal recessive metabolic disorder related to valine catabolism and results from variants in ACAD8. Here, we present the clinical, biochemical, and genotypes of seven patients with IBDHD in China for the first time. Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms. All patients showed remarkably increased concentrations of C4-aclycarnitine with elevated C4/C2 and C4/C3 ratios. In urine organic acid tests, only one patient presented with an increased concentration of isobutyrylglycine excretion. Genetic testing was performed to detect the causative variants. Five previously unreported variants, c.235C > G, c.286G > A, c.444G > T c.1092 + 1G > A, and c.1176G > T, and one known variant, c.1000C > T, in ACAD8 were identified. These previously unreported variants in ACAD8 were predicted to be disease-causing and the c.1092 + 1G > A variant was confirmed to cause skipping of exon 9 by reverse transcription PCR. The most common variant was c.286G > A, which showed an allelic frequency of 50% (7/14), and thus may be a prevalent variant among Chinese patients. Our results broaden the mutational spectrum of ACAD8 and improve the understanding of the clinical phenotype of IBDHD. Highlights • This is the first report of clinical, biochemical, and genetic study on isobutyryl-CoA dehydrogenase deficiency in China. • Five previously unreported variants in ACAD8 gene were identified. • The previously unreported splice variant was confirmed to cause skipping of exon 9 by RT-PCR. • A prevalent variant c.286G > A was identified among Chinese population. [ABSTRACT FROM AUTHOR]

We have functionally characterized the role of two putative mitochondrial enzymes in valine degradation using insertional mutants. Prior to this study, the relationship between branched-chain amino acid degradation (named for leucine, valine and isoleucine) and seed development was limited to leucine catabolism. Using a reverse genetics approach, we show that disruptions in the mitochondrial valine degradation pathway affect seed development and germination in Arabidopsis thaliana. A null mutant of 3-hydroxyisobutyryl-CoA hydrolase ( CHY4, At4g31810) resulted in an embryo lethal phenotype, while a null mutant of methylmalonate semialdehyde dehydrogenase ( MMSD, At2g14170) resulted in seeds with wrinkled coats, decreased storage reserves, elevated valine and leucine, and reduced germination rates. These data highlight the unique contributions CHY4 and MMSD make to the overall growth and viability of plants. It also increases our knowledge of the role branched-chain amino acid catabolism plays in seed development and amino acid homeostasis. [ABSTRACT FROM AUTHOR]

Background: Deficiency of 3-hydroxy-isobutyryl-CoA hydrolase (HIBCH) caused by HIBCH mutations is a rare cerebral organic aciduria caused by disturbance of valine catabolism. Multiple mitochondrial respiratory chain (RC) enzyme deficiencies can arise from a number of mechanisms, including defective maintenance or expression of mitochondrial DNA. Impaired biosynthesis of iron-sulphur clusters and lipoic acid can lead to pyruvate dehydrogenase complex (PDHc) deficiency in addition to multiple RC deficiencies, known as the multiple mitochondrial dysfunctions syndrome.Methods: Two brothers born to distantly related Pakistani parents presenting in early infancy with a progressive neurodegenerative disorder, associated with basal ganglia changes on brain magnetic resonance imaging, were investigated for suspected Leigh-like mitochondrial disease. The index case had deficiencies of multiple RC enzymes and PDHc in skeletal muscle and fibroblasts respectively, but these were normal in his younger brother. The observation of persistently elevated hydroxy-C4-carnitine levels in the younger brother led to suspicion of HIBCH deficiency, which was investigated by biochemical assay in cultured skin fibroblasts and molecular genetic analysis.Results: Specific spectrophotometric enzyme assay revealed HIBCH activity to be below detectable limits in cultured skin fibroblasts from both brothers. Direct Sanger sequence analysis demonstrated a novel homozygous pathogenic missense mutation c.950G Conclusions: HIBCH deficiency, a disorder of valine catabolism, is a novel cause of the multiple mitochondrial dysfunctions syndrome, and should be considered in the differential diagnosis of patients presenting with multiple RC deficiencies and/or pyruvate dehydrogenase deficiency. [ABSTRACT FROM AUTHOR]

Abstract: Significant evidence of the pharmacological and physiological effects of branched-chain amino acids (BCAA) has accumulated, attracting the interest of not only clinicians but also basic medical researchers. We summarize here the characteristic features of BCAA catabolism, focusing on the initial two enzymes in the pathway, branched-chain aminotransferase and branched-chain α-keto acid dehydrogenase complex. In addition, we describe a unique characteristic of the valine catabolic pathway. Finally, we present evidence obtained in animal studies that indicates that BCAA treatment may be appropriate for liver cirrhosis, but not acute liver failure. [Copyright &y& Elsevier]

3-Hydroxy-isobutyryl-coenzyme A (CoA) hydrolase (HBICH) deficiency is a rare cerebral organic aciduria caused by disturbance of valine catabolism that leads to the accumulation of toxic metabolites, methacrylyl-CoA. The major feature exhibited by a patient with HBICH deficiency includes multiple congenital malformations and abnormal neurologic findings. However, the pathophysiology of this disease remains unknown. The major treatment for HBICH deficiency involves a low-protein diet, especially restricting valine, supplemented with micronutrients and carnitine. To our knowledge, only four patients with HBICH deficiency have been reported. These patients were boys and presented with different clinical, biochemical, and genetic features than our patient. In this report, we described what was to our knowledge the first genetically confirmed girl with HBICH deficiency in China. A 5-mo nutritional intervention was given to the patient by a nutritional support team. On this regimen, the patient's symptoms were alleviated and her quality of life was improved., (Copyright © 2015 Elsevier Inc. All rights reserved.)