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Cyclic dipeptides are produced by organisms across all domains of life, with many exhibiting anticancer and antimicrobial properties. Oxidations are often key to their biological activities, particularly C-C bond oxidation catalysed by tailoring enzymes including cyclodipeptide oxidases. These flavin-dependent enzymes are underexplored due to their intricate three-dimensional arrangement involving multiple copies of two distinct small subunits, and mechanistic details underlying substrate selection and catalysis are lacking. Here, we determined the structure and mechanism of the cyclodipeptide oxidase from the halophile Nocardiopsis dassonvillei (NdasCDO), a component of the biosynthetic pathway for nocazine natural products. We demonstrated that NdasCDO forms filaments in solution, with a covalently bound flavin mononucleotide (FMN) cofactor at the interface between three distinct subunits. The enzyme exhibits promiscuity, processing various cyclic dipeptides as substrates in a distributive manner. The reaction is optimal at high pH and involves the formation of a radical intermediate. Pre-steady-state kinetics, a significant solvent kinetic isotope effect, and the absence of viscosity effects suggested that a step linked to FMN regeneration controlled the reaction rate. Our work elucidates the complex mechanistic and structural characteristics of this dehydrogenation reaction, positioning NdasCDO as a promising biocatalyst and expanding the FMN-dependent oxidase family to include enzyme filaments. Cyclodipeptide oxidases are filamentous enzymes. Here, the authors dissect the mechanism of a promiscuous flavoenzyme from the biosynthesis of cyclodipeptide natural products, unveiling fast catalysis for peptide oxidation in a distinct active site. [ABSTRACT FROM AUTHOR]

Hydroquinone 1,2-dioxygenase (HQDO), an enzyme involved in the catabolism of 4-hydroxyacetophenone in Pseudomonas fluorescens ACB, was purified to apparent homogeneity. Ligandation with 4-hydroxybenzoate prevented the enzyme from irreversible inactivation. HQDO was activated by iron(H) ions and catalyzed the ring fission of a wide range of hydroquinones to the corresponding 4-hydroxymuconic semialdehydes. HQDO was inactivated by 2,2'-dipyridyl, o-phenanthroline, and hydrogen peroxide and inhibited by phenolic compounds. The inhibition with 4-hydroxybenzoate ([K.sub.i] = 14 [micro]M) was competitive with hydroquinone. Online size-exclusion chromatographymass spectrometry revealed that HQDO is an [alpha]2[beta]2 heterotetramer of 112.4 kDa, which is composed of an [alpha]-subunit of 17.8 kDa and a [beta]-subunit of 38.3 kDa. Each [beta]-subunit binds one molecule of 4-hydroxybenzoate and one iron(II) ion. N-terminal sequencing and peptide mapping and sequencing based on matrix-assisted laser desorption ionization--two-stage time of flight analysis established that the HQDO subunits are encoded by neighboring open reading frames (hapC and hapD) of a gene cluster, implicated to be involved in 4-hydroxyacetophenone degradation. HQDO is a novel member of the family of nonheme-iron(II)-dependent dioxygenases. The enzyme shows insignificant sequence identity with known dioxygenases.

We modified and optimized a first generation quadrupole time-of-flight (Q-TOF) 1 to perform tandem mass spectrometry on macromolecular protein complexes. The modified instrument allows isolation and subsequent dissociation of high-mass protein complexes through collisions with argon molecules. The modifications of the Q-TOF 1 include the introduction of (1) a flow-restricting sleeve around the first hexapole ion bridge, (2) a low-frequency ion-selecting quadrupole, (3) a high-pressure hexapole collision cell, (4) high-transmission grids in the multicomponent ion lenses, and (5) a low repetition rate pusher. Using these modifications, we demonstrate the experimental isolation of ions up to 12 800 mass-to-charge units and detection of product ions up to 38 150 Da, enabling the investigation of the gas-phase stability, protein complex topology, and quaternary structure of protein complexes. Some of the data reveal a so-far unprecedented new mechanism in gas-phase dissociation of protein oligomers whereby a tetramer complex dissociates into two dimers. These data add to the current debate whether gas-phase structures of protein complexes do retain some of the structural features of the corresponding species in solution. The presented low-cost modifications on a Q-TOF 1 instrument are of interest to everyone working in the fields of macromolecular mass spectrometry and more generic structural biology.

Ion mobility mass spectrometry (IM-MS) is used for studying several chaperonin complexes that can be present during substrate folding. The studies have shown that the charge state reduction has not affected the relative differences seen in collision cross sections for the chaperonin assemblies.

The yeast Ski complex assists the exosome in the degradation of mRNA. The Ski complex consists of three components; Ski2, Ski3, and Ski8, believed to be present in a 1:1:1 stoichiometry. Measuring the mass of intact isolated endogenously expressed Ski complexes by native mass spectrometry we unambiguously demonstrate that the Ski complex has a hetero-tetrameric stoichiometry consisting of one copy of Ski2 and Ski3 and two copies of Ski8. To validate the stoichiometry of the Ski complex, we performed tandem mass spectrometry. In these experiments one Ski8 subunit was ejected concomitant with the formation of a Ski2/Ski3/Ski8 fragment, confirming the proposed stoichiometry. To probe the topology of the Ski complex we disrupted the complex and mass analyzed the thus formed subcomplexes, detecting Ski8-Ski8, Ski2-Ski3, Ski8-Ski2, and Ski8-Ski8-Ski2. Combining all data we construct an improved structural model of the Ski complex. [ABSTRACT FROM AUTHOR]

Objective: Roux-en-Y gastric bypass (RYGB) surgery has been shown to lead to favourable health outcomes in obese patients. However, the molecular changes that occur and how they relate to clinical measures are poorly understood. Here, we characterise the proteomic alterations that occur in plasma of RYGB patients before and 9 months after surgery using quantitative proteomics., Methods: Plasma proteomics was performed by sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) to identify and quantify differentially abundant proteins. Relationships between significantly altered proteins and clinical markers were examined. A gene set enrichment analysis was also conducted to identify altered pathways., Results: From the proteomic analysis, 27 proteins increased, and 43 proteins decreased in abundance 9 months after surgery, providing insights into the physiological changes that accompany weight loss. Proteins including sex hormone binding globulin (SHBG), inter-alpha-trypsin inhibitor heavy chain 3 (ITIH3) and apolipoprotein D (APOD), which increased in abundance post-surgery, highlight improvements in lipid regulation, insulin sensitivity and inflammation. Proteins involved in coagulation, including α2-macroglobulin, kallikrein-B1, prothrombin, and factor (FX, FXI and FXII), exhibited reduced levels, aligning with a decrease in thrombotic potential., Conclusions: These findings provide a mechanistic understanding of how bariatric surgery leads to systemic changes in metabolic and haemostatic pathways, thus favourably modulating the risk of developing cardiovascular disease., (© 2025 The Author(s). Diabetes, Obesity and Metabolism published by John Wiley & Sons Ltd.)

Structural, functional and molecular cardiac defects have been reported in spinal muscular atrophy (SMA) patients and mouse models. Previous quantitative proteomics analyses demonstrated widespread molecular defects in the severe Taiwanese SMA mouse model. Whether such changes are conserved across different mouse models, including less severe forms of the disease, has yet to be established. Here, using the same high-resolution proteomics approach in the less-severe Smn2B/- SMA mouse model, 277 proteins were found to be differentially abundant at a symptomatic timepoint (post-natal day (P) 18), 50 of which were similarly dysregulated in severe Taiwanese SMA mice. Bioinformatics analysis linked many of the differentially abundant proteins to cardiovascular development and function, with intermediate filaments highlighted as an enriched cellular compartment in both datasets. Lamin A/C was increased in the cardiac tissue, whereas another intermediate filament protein, desmin, was reduced. The extracellular matrix (ECM) protein, elastin, was also robustly decreased in the heart of Smn2B/- mice. AAV9-SMN1-mediated gene therapy rectified low levels of survival motor neuron protein and restored desmin levels in heart tissues of Smn2B/- mice. In contrast, AAV9-SMN1 therapy failed to correct lamin A/C or elastin levels. Intermediate filament proteins and the ECM have key roles in cardiac function and their dysregulation may explain cardiac impairment in SMA, especially since mutations in genes encoding these proteins cause other diseases with cardiac aberration. Cardiac pathology may need to be considered in the long-term care of SMA patients, as it is unclear whether currently available treatments can fully rescue peripheral pathology in SMA., (© The Author(s) 2023. Published by Oxford University Press.)

The yeast Ski complex assists the exosome in the degradation of mRNA. The Ski complex consists of three components; Ski2, Ski3, and Ski8, believed to be present in a 1:1:1 stoichiometry. Measuring the mass of intact isolated endogenously expressed Ski complexes by native mass spectrometry we unambiguously demonstrate that the Ski complex has a hetero-tetrameric stoichiometry consisting of one copy of Ski2 and Ski3 and two copies of Ski8. To validate the stoichiometry of the Ski complex, we performed tandem mass spectrometry. In these experiments one Ski8 subunit was ejected concomitant with the formation of a Ski2/Ski3/Ski8 fragment, confirming the proposed stoichiometry. To probe the topology of the Ski complex we disrupted the complex and mass analyzed the thus formed subcomplexes, detecting Ski8-Ski8, Ski2-Ski3, Ski8-Ski2, and Ski8-Ski8-Ski2. Combining all data we construct an improved structural model of the Ski complex.