­­OmpF porins of Enterobacteriaceae possess amyloidogenic properties

Outer membrane porins represent an important group of bacterial virulence associated proteins, whose amyloidogenic properties are actively investigated. Amyloids are protein fibrils with highly ordered beta-sheet-rich spatial structure and unique physicochemical properties including unusual resistance to treatment with different detergents and proteases. In prokaryotes, at least ten different functional groups of functional amyloids have been identified. Several outer membrane porins of gram-negative bacteria were shown to adopt amyloid state. In this study, we analyzed amyloid properties of the OmpF porins of Escherichia coli and Salmonella enteritidisspecies which are known to be associated with the virulence and pathogenic properties of these bacteria in humans and animals. Our data show that recombinant OmpF proteins form fibrils with morphology typical for amyloids. The in vitro obtained aggregates of OmpF demonstrate resistance to treatment with cold ionic detergents and proteases. Moreover, these aggregates bind amyloid-specific dye thioflavin T and exhibit apple-green birefringence in polarized light upon staining with Congo Red dye. Overall, these data confirm the amyloidogenic properties of the OmpF porins of E. coli and S. enteritidis in vitroand suggest that these proteins could represent novel functional bacterial amyloids probably associated with pathogen-host interactions.