Ultraweak interactions drive cap-mediated positioning and elongation of the bacterial flagellar filament.

ABSTRACT: The bacterial flagellum, essential for motility and pathogenesis, requires the filament cap (FliD) to polymerize flagellin (FliC). However, the mechanisms governing the transition from the hook junction to the filament elongation remain elusive, obscured by stoichiometric mismatches and barely detectable interactions. To resolve this, we deploy solution NMR to characterize ultra-weak interactions, quantify affinities (K_D ≈ 0.1 mM for junction protein FlgL; 1.65 mM for FliC). These data enable rational complex stabilization for cryo-EM structure determination of Salmonella FliD pentamers complexed with FlgL or FliC, revealing that both substrates engage an identical conserved surface in a 5:5 stoichiometry. Integrating these structures into native flagellar tip densities reveal a

SUBMITTER: Chen L 

PROVIDER: S-EPMC12855180 | biostudies-literature | 2025 Dec

REPOSITORIES: biostudies-literature