Llarrull, L. I. | Search bioRxiv

bioRxiv2026

Redox-regulated cysteine acylation governs β-lactam sensing by the Vibrio histidine kinase VbrK

The ability of pathogens to develop resistance mechanisms makes the continuous search for novel therapeutic targets indispensable. Resistance-activating systems are promising targets for restoring the efficacy of existing antibiotics. VbrK/VbrR is a two-component system from Vibrio parahaemolyticus reported as the first sensing system in gram-negatives that directly detects {beta}-lactam antibiotics. {beta}-Lactam-induced activation of this system results in the expression of the serine {beta}-lactamase CARB. In this study, we provide insights into the mechanism of {beta}-lactam binding to the periplasmic sensor domain of the histidine kinase VbrK. Our results demonstrate that the interaction depends on the redox state of cysteines C86 and C107, highlighting the role of disulfide bond dynamics in modulating ligand recognition. We further show that formation of a non-covalent complex leads to acylation of the sensor domain by {beta}-lactams, a modification that is slowly reversed through de-acylation, yielding the hydrolyzed {beta}-lactam ring and allowing for recovery from induction once the antibiotic has been depleted from the environment. Together, these findings reveal a previously unrecognized redox- and covalent chemistry-dependent mode of {beta}-lactam interaction with histidine kinases, providing a molecular framework to understand how VbrK detects and responds to {beta}-lactam antibiotics, and opening new avenues to prevent manifestation of resistance. Short broader audience statementBacterial pathogens can sense the presence of antibiotics and trigger resistance responses, making infections increasingly difficult to treat. In this study, we uncover a previously unknown mechanism by which {beta}-lactam antibiotics interact with a sensor protein that activates resistance in Vibrio parahaemolyticus. These findings pave the way for designing new compounds that can block this interaction and thus restore the effectiveness of {beta}-lactam antibiotics against gastrointestinal infections caused by resistant bacteria.

microbiology↗

bioRxiv2025

The histidine kinase VraS orchestrates the cell-wall stress response in Staphylococcus aureus via its direct interaction with glycopeptides and β-lactams

Multidrug-resistant Staphylococcus aureus is a major global health threat, with the VraTSR three-component system playing a key role in sensing and conferring resistance to cell-wall active antibiotics, particularly vancomycin. VraTSR comprises the membrane histidine kinase VraS, the cytoplasmic response regulator VraR, and the uncharacterized membrane protein VraT, which regulate the cell wall stress stimulon. However, the molecular signals sensed by VraTSR remain unknown. To elucidate the activation mechanism of this regulatory system, we investigated interactions with {beta}-lactams and glycopeptides. Using a transcriptional reporter strain, we confirmed VraTSR activation by {beta}-lactams, glycopeptides, a vancomycin-derived photoprobe (VPP), and the previously unreported activators A47934 and moenomycin A. Photo-crosslinking assays with VPP and full-length VraS expressed in membranes revealed a direct interaction with vancomycin, which was further confirmed in purified VraS reconstituted in liposomes. VPP binding was concentration-dependent, saturable, and displaced by vancomycin. Saturation transfer difference (STD) Nuclear Magnetic Resonance (NMR) experiments confirmed vancomycin binding to VraS and demonstrated ampicillin interaction, highlighting the involvement of aryl protons from both antibiotics. These findings establish VraS as a receptor for vancomycin and ampicillin. In contrast, assays with membrane vesicles expressing only VraT or co-expressing VraS/VraT did not show covalent adduct formation between VraT and VPP. While VraTs exact role remains unclear, its participation in antibiotic sensing or signal transduction cannot yet be excluded. These results demonstrate that vancomycin and ampicillin directly activate VraS, providing critical insights into the activation of the cell wall stress stimulon and the mechanisms underlying antibiotic resistance. Disrupting VraTSR signaling is a promising strategy to combat multidrug resistance in S. aureus, and we provide invaluable in vitro platforms for identifying potential VraS inhibitors. Author SummaryMultidrug-resistant Staphylococcus aureus poses a major global health threat due to its resistance to cell-wall active antibiotics. Our study focuses on the VraTSR three-component system, a key regulator of the cell wall stress response in S. aureus, whose activation signals have remained unknown. We demonstrate that VraS, the membrane histidine kinase of the system, acts as a direct receptor for vancomycin and ampicillin--two structurally distinct antibiotics. These findings uncover the activation mechanism of VraTSR and position VraS as a central player in antibiotic sensing and resistance. By identifying VraS as a direct antibiotic receptor, we provide a promising target for developing inhibitors to disrupt VraTSR signaling and restore antibiotic efficacy. Additionally, the in vitro platforms we established enable the identification and testing of potential VraS inhibitors. This study highlights the importance of understanding bacterial stress-response pathways to combat antibiotic resistance, offering critical insights for developing new therapeutic strategies against multidrug-resistant S. aureus, a growing global health challenge.

biochemistry↗