Biology subjects

Seravalli, J.

Publications and source records attributed to Seravalli, J..

4 recordsLinked to original sources

bioRxiv2025

Cadmium toxicity to the human gut microbiome varies depending on composition

Cadmium (Cd(II), hereafter Cd) is a toxic heavy metal with detrimental impacts on the gut microbiota. We investigated the effects of acute Cd exposure on human fecal microbiotas using 24-hour in vitro cultures from 21 healthy adult donors. Regression analysis of butyrate production in the absence (-Cd) versus presence (+Cd) of Cd identified three categories of microbial responses: sensitive, intermediate, and resilient. Under Cd stress, sensitive microbiomes exhibited significant decreases in butyrate coupled with elevated acetate and lactate production, while resilient microbiomes did not show significant changes in butyrate and exhibited attenuated increases in lactate compared with sensitive microbiomes. Several genera were significantly different between sensitive and resilient communities after exposure to Cd, but the most striking was Anaerostipes. Network analysis revealed a significantly greater disruption of microbial interactions in sensitive communities compared with resilient. In resilient communities, butyrate production was primarily associated with Faecalibacterium in the absence of Cd and Anaerostipes in the presence of Cd. Furthermore, supplementation of sensitive microbiota with Anaerostipes species restored butyrate production in the presence of Cd. These findings highlight distinct gut microbial responses to acute Cd exposure and provide a foundation to investigate microbiota features underlying Cd sensitivity or resilience. IMPORTANCECadmium is a widespread environmental contaminant that reaches the human intestine, where it can disrupt the gut microbial community and negatively impact digestive and systemic health. However, this study demonstrates that human gut microbiomes vary in their responses to cadmium exposure: sensitive communities exhibit losses of beneficial organisms, particularly butyrate-producing taxa that contribute to intestinal integrity and metabolic balance, whereas resilient communities retain microorganisms with this key functional capacity. Anaerostipes appeared to be involved, at least in part, with Cd resilience. This work advances our understanding of how gut microbial functions may mitigate the adverse effects of cadmium exposure by identifying the compositional features that distinguish sensitive from resilient microbiomes. These findings highlight the importance of elucidating microbiome-mediated mechanisms that help sustain host health and lay the groundwork for deeper mechanistic studies aimed at mitigating cadmium toxicity.

microbiology↗

bioRxiv2025

Aromatic Patch in WhiB-Like Transcription Factors Facilitates Primary Sigma Factor Interaction in Mycobacterium tuberculosis

WhiB-like (Wbl) family proteins are a unique family of iron-sulfur ([4Fe-4S]) cluster-bound transcription factors found exclusively in Actinobacteria and actinobacteriophages, including the notoriously persistent pathogen Mycobacterium tuberculosis (Mtb). Despite their critical roles in cell development, stress response and antibiotic resistance, the mechanisms of gene regulation by the Wbl family proteins are not fully understood due to the lack of a canonical DNA-binding motif in most Wbl proteins. Here, we present structural and biochemical evidence demonstrating that all Mtb Wbl proteins bind to the same site in the conserved region 4 of the primary sigma 70 factor facilitated by a previously unrecognized structural motif, the aromatic patch, in the Wbl family. Our phylogenetic findings provide compelling evidence for a complex evolutionary relationship of Wbls between actinobacteria and the associated phages. Together, this work fills a critical gap in our understanding of the function, mechanism and evolutionary origin of Wbls.

biochemistry↗

bioRxiv2023

Cobalt-sulfur coordination chemistry drives B12 loading onto methionine synthase

Cobalt-sulfur (Co-S) coordination is labile to both oxidation and reduction chemistry and is rarely seen in Nature. Cobalamin (or vitamin B12) is an essential cobalt-containing organometallic cofactor in mammals, and is escorted via an intricate network of chaperones to a single cytoplasmic target, methionine synthase. In this study, we report that the human cobalamin trafficking protein, MMADHC, exploits the chemical lability of Co-S coordination, for cofactor off-loading onto methionine synthase. Cys-261 on MMADHC serves as the {beta}-axial ligand to cobalamin. Complex formation between MMADHC and methionine synthase is signaled by loss of the lower axial nitrogen ligand, leading to five-coordinate thiolato-cobalamin. Nucleophilic displacement by the vicinal thiolate, Cys-262, completes cofactor transfer to methionine synthase and release of a cysteine disulfide-containing MMADHC. The physiological relevance of this mechanism is supported by clinical variants of MMADHC, which impair cofactor binding and off-loading, explaining the molecular basis of the associated homocystinuria.

biochemistry↗

bioRxiv2019

Cysteine modification can gate non-equilibrium conformational dynamics during enzyme catalysis

Summary ParagraphProtein dynamics play an important role in enzyme catalysis1-4. Many enzymes form covalent catalytic intermediates that can alter enzyme structure and conformational dynamics5,6. How these changes in enzyme structure and dynamics facilitate passage along the reaction coordinate is a fundamental unanswered question in structural enzymology. Here, we use Mix-and-Inject Serial Femtosecond X-ray Crystallography (MISC) at an X-ray Free Electron Laser (XFEL)7-10, ambient temperature X-ray crystallography, computer simulations, and enzyme kinetics to characterize how covalent modification of the active site cysteine residue in isocyanide hydratase (ICH) alters the enzymes conformational ensemble throughout the catalytic cycle. With MISC, we directly observe formation of a thioimidate covalent intermediate during ICH catalysis. The intermediate exhibits changes in the active site electrostatic environment, disrupting a hydrogen bond and triggering a cascade of conformational changes in ICH. X-ray-induced formation of a cysteine-sulfenic acid at the catalytic nucleophile (Cys101-SOH) with conventional crystallography at ambient temperature induces similar conformational shifts, demonstrating that these enzyme motions result from cysteine modification. Computer simulations show how cysteine modification-gated structural changes allosterically propagate through the ICH dimer. Mutations at Gly150 that modulate helical mobility reduce ICH catalytic turnover and alter its pre-steady state kinetic behavior, establishing that helical mobility is important for ICH catalytic efficiency. Taken together, our results demonstrate the potential of mix-and-inject XFEL crystallography to capture otherwise elusive mechanistic details of enzyme catalysis and dynamics from microcrystalline samples7,11. This approach can connect conformational dynamics to function for the large class of systems that rely on covalently modified cysteine residues for catalysis or regulation, resolving long-standing questions about enzyme mechanism and functionally relevant non-equilibrium enzyme motions.

biochemistry↗