Biology subjects

Shah, N. B.

Publications and source records attributed to Shah, N. B..

3 recordsLinked to original sources

bioRxiv2025

Methicillin-Resistant Staphylococcus aureus has Phenotypic Variation in mecA Expression that Alters Antibiotic Sensitivity

Methicillin resistant Staphylococcus aureus (MRSA) sepsis has a high rate of morbidity and mortality. Multiple clinical studies have demonstrated improved outcomes when MRSA sepsis is treated with dual antibiotic therapy that includes a {beta}-lactam antibiotic such as cefazolin. This is a paradox as MRSA should be inherently resistant to this class of antibiotics. We report a serendipitous observation revealed a phenotype where MRSA became sensitive to cefazolin when cultured in a physiologic relevant media of fetal bovine serum as well as in synovial fluid. This could be observed across multiple clinical isolates. Expected resistance was maintained when cultured in Muller Hinton Broth (MHB). MRSA {beta}-lactam antibiotic resistance is mediated by PBP2a, a penicillin-binding protein encoded by mecA. We hypothesized that this phenotype of antibiotic sensitivity in physiologic medium was based, in part, on levels of PBP2a expression and post-translational modifications of peptidoglycan wall teichoic acid (WTA). We therefore conducted quantitative RT-PCR analysis and Western blotting which demonstrated limited mecA expression in the mRNA level and limited PBP2a protein level when cultured in FBS or synovial fluid as compared to the clinical microbiology standard MHB, respectively. Whole genome sequencing of loss of function mutants generated through serial passaging in FBS revealed that the clp family of proteins and rpo genes were involved in {beta}-lactam resistance. Cell wall peptidoglycan analysis suggested that WTA glycosylation was altered between {beta}-lactam resistant and sensitive MRSA phenotypes. Together, this suggests pathways for clpP, rpoB, and WTA glycosylation can be new potential targets for MRSA treatment. IMPORTANCEThis study demonstrates that MRSA has phenotypic variation in mecA expression, PBP2a protein levels, and patterns of wall teichoic acid glycosylation based on environmental conditions which can result in a phenotype of {beta}-lactam antibiotic sensitivity. The presence of an antibiotic resistance gene does not necessarily result in antibiotic resistance. This provides a possible explanation for the clinical observations of potential therapeutic benefit of {beta}-lactam antibiotics in dual therapy treatment of MRSA sepsis and suggests new therapeutic strategies to combat multidrug resistant bacteria. More importantly, identifying genes potentially responsible for this phenotype offers new potential therapeutic targets for the treatment of multidrug resistant infection.

microbiology↗

bioRxiv2021

3D structure and in situ arrangements of CatSper channel in the sperm flagellum

The sperm calcium channel CatSper plays a central role in successful fertilization as a primary Ca2+ gateway into the sperm flagellum. However, CatSpers complex subunit composition has impeded its reconstitution in vitro and structural elucidation. Here, we applied cryo-electron tomography to visualize the macromolecular organization of the native CatSper channel complex in intact mammalian sperm, as well as identified three additional CatSper-associated proteins. The repeating CatSper units form long zigzag-rows in four nanodomains along the flagella. In both mouse and human sperm, each CatSper repeat consists of a tetrameric pore complex. Murine CatSper contains an additional outwardly directed wing-structure connected to the tetrameric channel. The majority of the extracellular domains form a canopy above each pore-forming channel that interconnects to a zigzag-shaped roof. The intracellular domains link two neighboring channel complexes to a diagonal array. The loss of this intracellular link in Efcab9-/- sperm distorts the longitudinally aligned zigzag pattern and compromises flagellar movement. This work offers unique insights into the mechanisms underlying the assembly and transport of the CatSper complex to generate the nanodomains and provides a long-sought structural basis for understanding CatSper function in the regulation of sperm motility.

biophysics↗

bioRxiv2017

Phasic Activation of Ventral Tegmental, but not Substantia Nigra, Dopamine Neurons Promotes Model-Based Pavlovian Reward Learning

Dopamine (DA) neurons in the ventral tegmental area (VTA) and substantia nigra (SNc) encode reward prediction errors (RPEs) and are proposed to mediate error-driven learning. However the learning strategy engaged by DA-RPEs remains controversial. Model-free associations imbue cue/actions with pure value, independently of representations of their associated outcome. In contrast, model-based associations support detailed representation of anticipated outcomes. Here we show that although both VTA and SNc DA neuron activation reinforces instrumental responding, only VTA DA neuron activation during consumption of expected sucrose reward restores error-driven learning and promotes formation of a new cue[->]sucrose association. Critically, expression of VTA DA-dependent Pavlovian associations is abolished following sucrose devaluation, a signature of model-based learning. These findings reveal that activation of VTA-or SNc-DA neurons engages largely dissociable learning processes with VTA-DA neurons capable of participating in model-based predictive learning, while the role of SNc-DA neurons appears limited to reinforcement of instrumental responses.

neuroscience↗