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bioRxiv · 10.64898/2026.08.05.742979

Bacteroidales Secreted Antimicrobial Protein-1 receptor recognition is coupled to protease-activation to form bactericidal pores.

Mostyn, S. N.·Flores, K.·Hedger, G.·Nagaraj, H.·Rouse, S. L.·Comstock, L. E.·Bubeck, D.
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Abstract

Bacteroidales secreted antimicrobial proteins (BSAPs) are diffusible MACPF-domain toxins that mediate intra-species antagonism in the gut microbiota. Here we define the mechanism of action of BSAP-1 from Bacteroides fragilis, showing how target specificity encoded within the N- and C-terminal domains is coordinated with pore-forming activity of the MACPF. We show that specificity of the toxin for its receptor is mediated by an extended interface comprised of the BSAP-1 C-terminal domain and residues on the receptor that differ from the orthologous protein of BSAP-1 producing strains. On the surface of susceptible cells, BSAP-1 undergoes proteolytic cleavage of an N-terminal regulatory domain, triggering its assembly into oligomeric pores. Cryo-electron microscopy of membrane-inserted BSAP-1 reveals a 13-subunit transmembrane {beta}-barrel pore formed through canonical MACPF rearrangements. Comparative modelling supports a conserved oligomerization mechanism across the BSAP family despite diversification of receptor-binding domains that target either proteins or glycan receptors. Together, these findings establish BSAP-1 as a receptor-targeted, protease-activated antibacterial MACPF toxin and provide a framework for understanding how gut Bacteroidales spatially restrict toxin activation to shape strain-level competition.

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Mostyn, S. N., Flores, K., Hedger, G., Nagaraj, H., Rouse, S. L., Comstock, L. E., Bubeck, D.. 2026-08-05. Bacteroidales Secreted Antimicrobial Protein-1 receptor recognition is coupled to protease-activation to form bactericidal pores.. https://doi.org/10.64898/2026.08.05.742979

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