Riestra, A. M. | bioRxiv Science

bioRxiv2026

Study of microbe-microbe interactions between the sexually transmitted parasite Trichomonas vaginalis with the cervicovaginal bacteria Lactobacillus iners

Trichomonas vaginalis is the leading cause of non-viral sexually transmitted infections and it is associated with comorbidities that affect female health. Lactobacillus iners is one of the most predominant bacteria in the cervicovaginal microbiome. As so, both microbes are likely to encounter one another upon T. vaginalis infection. To our knowledge, the interaction of both microbes has not been previously investigated. Here, we report that T. vaginalis and L. iners bind to one another at early time points of co-incubation. Using imaging flow cytometry and scanning electron microscopy, we capture the dynamics of this microbe-microbe association. We observed active remodeling of the T. vaginalis cell surface leading to thin-membrane protrusions that make contact with L. iners. Larger T. vaginalis membrane extensions that surround and engulf L. iners were also visible. These T. vaginalis-L. iners interactions ultimately lead to a reduction of L. iners viability while T. vaginalis viability was unaffected by exposure to L. iners. Inhibition of actin polymerization blocked T. vaginalis antibacterial activity against L. iners. Together our findings reveal novel insight about T. vaginalis-L. iners interactions and highlight a new T. vaginalis pathogenic effect.

microbiology↗

bioRxiv2025

Quantitative Membrane Binding Assays Reveal an Inhibitory Role for the BRAF-Specific Region in CRD and Lipid Interaction

BRAF is a serine/threonine kinase and a central effector of the mitogen-activated protein kinase (MAPK) signaling pathway, frequently mutated in cancer. Its activation is tightly controlled by autoinhibitory mechanisms that regulate membrane recruitment and dimerization. The BRAF-specific region (BSR), located at the N-terminus, is known to promote isoform-preferred RAS binding and facilitate dimerization with kinase suppressor of RAS (KSR), yet its role in regulating lipid interaction has remained unexplored. Here, we identify the BSR as a previously unrecognized inhibitory module that attenuates lipid binding by the cysteine-rich domain (CRD). Using quantitative in vitro reconstitution with supported lipid bilayers and fluorescence microscopy, we demonstrate that the BRAF CRD exhibits high intrinsic affinity for phosphatidylserine-rich membranes, but the inclusion of the BSR markedly reduces the membrane binding. We further demonstrate that the inhibitory function of the BSR correlates with its global electrostatic properties rather than a single defined sequence motif. This inhibitory effect of BSR was corroborated in live cells by quantifying plasma membrane localization of BRAF constructs, including the full-length protein. When canonical autoinhibition of CRD--mediated by sequestration within the 14-3-3 dimer--is disrupted by oncogenic mutation or RAF inhibitor treatment, the BSR assumes a compensatory role in repressing CRD-lipid interaction. This additional regulatory layer provided by the BSR prevents RAS-independent membrane recruitment under both physiological and pathological conditions. Broad Impact StatementProtein-lipid interactions are a fundamental mechanism for regulating the localization and activity of signaling proteins. This study reveals that the N-terminal segment of BRAF acts as an inhibitory module that suppresses lipid engagement by CRD, particularly when canonical autoinhibition is disrupted by oncogenic mutation or inhibitor treatment. This additional layer of regulation provides new insight into BRAF membrane dynamics and may have implications in therapeutic intervention of dysregulated BRAF signaling.

biochemistry↗