Biology subjects

Brown, M. H.

Publications and source records attributed to Brown, M. H..

3 recordsLinked to original sources

bioRxiv2026

Structural basis of drug efflux by the staphylococcal efflux pump QacA

The QacA DHA2 exporter from Staphylococcus aureus is a prototypical multidrug transporter that, like other bacterial efflux pumps, can extrude a wide range of cytotoxic compounds thus playing a crucial role in antimicrobial resistance. Here, we report crystal structures of wild-type QacA in three key conformational states: inward-open, outward-open and ethidium-bound, representing the first ligand-bound structure of a 14 transmembrane helices (TM) DHA2 transporter. In combination with computational and functional studies, these structures provide a mechanistic framework to understand drug recognition and extrusion. Structural analyses reveal remarkable adaptability within the binding pocket, including a ligand-induced deformation of TM5 that enables coordination of ethidium bromide in the outward-open state. Molecular dynamics simulations show spontaneous lipid entry into the transporter core and suggest that substrate binding from the inner membrane leaflet initiates a conformational transition to an outward-open state, stabilizing high-affinity interactions. Subsequent binding site protonation drives substrate extrusion. Together, these findings elucidate the structural dynamics and mechanistic underpinnings of QacA-mediated multidrug transport, highlighting conformational flexibility and proton-coupled electrostatic changes as key determinants of multidrug recognition and extrusion. This study provides a foundational framework for developing targeted inhibitors to combat bacterial multidrug resistance.

biochemistry↗

bioRxiv2023

Testing the predictive performance of comparative extinction risk models to support the global amphibian assessment

Assessing the extinction risk of species through the IUCN Red List is key to guiding conservation policies and reducing biodiversity loss. This process is resource-demanding, however, and requires a continuous update which becomes increasingly difficult as new species are added to the IUCN Red List. The use of automatic methods, such as comparative analyses to predict species extinction risk, can be an efficient alternative to maintaining up to date assessments. Using amphibians as a study group, we predict which species were more likely to change status, in order to suggest species that should be prioritized for reassessment. We used species traits, environmental variables, and proxies of climate and land-use change as predictors of the IUCN Red List category of species. We produced an ensemble prediction of IUCN Red List categories by combining four different model algorithms: Cumulative Link Models (CLM), phylogenetic Generalized Least Squares (PGLS), Random Forests (RF), Neural Networks (NN). By comparing IUCN Red List categories with the ensemble prediction, and accounting for uncertainty among model algorithms, we identified species that should be prioritized for future reassessments due to high prediction versus observation mismatch. We found that CLM and RF performed better than PGLS and NN, but there was not a clear best algorithm. The most important predicting variables across models were species range size, climate change, and landuse change. We propose ensemble modelling of extinction risk as a promising tool for prioritizing species for reassessment while accounting for inherent models uncertainty.

ecology↗

bioRxiv2020

Conformational surveillance of Orai1 by a rhomboid intramembrane protease prevents inappropriate CRAC channel activation

Calcium influx through plasma membrane calcium release-activated calcium (CRAC) channels, which are formed of hexamers of Orai1, is a potent trigger for many important biological processes, most notably in T cell mediated immunity. Through a bioinformatics-led cell biological screen, we have identified Orai1 as a substrate for the rhomboid intramembrane protease, RHBDL2. We show that RHBDL2 prevents stochastic signalling in unstimulated cells through conformational surveillance and cleavage of inappropriately activated Orai1. A conserved, disease-linked proline residue is responsible for RHBDL2 recognising only the active conformation of Orai1, and cleavage by RHBDL2 is required to sharpen switch-like signalling triggered by store-operated calcium entry. Loss of RHBDL2 control of Orai1 causes severe dysregulation of CRAC channel effectors including transcription factor activation, inflammatory cytokine expression and T cell activation. We propose that this seek-and-destroy function may represent an ancient activity of rhomboid proteases in degrading unwanted signalling proteins.

biochemistry↗