Mating pair stabilization mediates bacterial conjugation species specificity

Abstract

Bacterial conjugation mediates contact-dependent transfer of DNA from donor to recipient bacteria, thus facilitating the spread of virulence and resistance plasmids. Here we describe how variants of the plasmid-encoded donor outer membrane (OM) protein TraN cooperate with distinct OM receptors in recipients to mediate mating pair stabilization and efficient DNA transfer. We show that TraN from the plasmids pKpQIL (Klebsiella pneumoniae), R100-1 (Shigella flexneri) and pSLT (Salmonella Typhimurium), and the prototypical F plasmid (Escherichia coli) interact with OmpK36, OmpW and OmpA, respectively. Cryo-EM analysis revealed that TraN pKpQIL interacts with OmpK36 through the insertion of a β-hairpin in the tip of TraN into a monomer of the OmpK36 trimer. Combining bioinformatic analysis with AlphaFold structural predictions, we identified a fourth TraN structural variant that mediates mating pair stabilization by binding OmpF. Accordingly, we devised a classifica- tion scheme for TraN homologues on the basis of structural similarity and their associated receptors: TraNα (OmpW), TraNβ (OmpK36), TraNγ (OmpA), TraNδ (OmpF). These TraN-OM receptor pairings have real-world implications as they reflect the distribution of resistance plasmids within clinical Enterobacteriaceae isolates, demonstrating the importance of mating pair stabilization in mediating conjugation species specificity. These findings will allow us to predict the distribution of emerging resistance plasmids in high-risk bacterial pathogens.