Intimin and Invasin Export Their C-Terminus to the Bacterial Cell Surface Using an Inverse Mechanism Compared to Classical Autotransport

Abstract

Invasin and intimin are major virulence factors of enteropathogenic Yersiniae and Escherichia coli, mediating invasion into and intimate adherence to host cells, respectively. Several studies have hinted that extracellular portion of these homologous proteins might be exported via an autotransport mechanism, but rigorous experimental proof has been lacking. Here, we present a topology model for invasin and intimin, consistent with the hypothesis that the N-terminal β-barrel domain acts as a translocation pore to secrete the C-terminal passenger domain. We confirmed this topology model by inserting epitope tags into the loops of the β-barrel. We further show that obstructing the pore of β-barrel hinders the export of the passenger domain. As for classical autotransport, the biogenesis of invasin and intimin is dependent on the Bam complex and the periplasmic chaperone SurA, whereas the chaperone/protease DegP is involved in quality control. However, compared to classical autotransporters (Type Va secretion), the domain structure of intimin and invasin is inverted. We conclude that proteins of the intimin and invasin family constitute a novel group of autotransported proteins, and propose that this class of autotransporters be termed Type Ve secretion.

Demarcating SurA Activities Required for Outer Membrane Targeting of Yersinia pseudotuberculosis Adhesins

“…Hence, inferior invasin assembly may also be amplified by a compromised BAM complex assembly platform. This correlates with a recent study published while our manuscript was in preparation that reported how Y. enterocolitica-derived invasin ectopically expressed in an E. coli surA deletion mutant failed to assemble in the OM (57). Interestingly, in this surrogate experimental setup, BamA was also deemed to be necessary for surface localization of invasin.…”

“…Invasin is an AT, although its secretion utilizes an inverse mechanism compared to classical (type Va secretion) autotransport (57). Similar to type Va secretion substrates, invasin is translocated from the cytoplasm across the inner membrane via the Sec translocase (58).…”

“…Similar to type Va secretion substrates, invasin is translocated from the cytoplasm across the inner membrane via the Sec translocase (58). However, the N-terminal domain of invasin forms the ␤-barrel in the OM (57). Type V secretion is also thought to involve BamA and various periplasmic chaperones (1, 13, 52, 59, 60, 61).…”

An outer membrane channel protein of Mycobacterium tuberculosis with exotoxin activity

“…This protein architecture resembles the intimin/invasin family of autotransporters from Gram-negative bacteria (47). Autotransporters facilitate translocation of a passenger domain via an integral outer membrane β-barrel domain (47)(48)(49)(50) and have been identified in virtually all pathogenic Gram-negative bacteria. They frequently translocate toxic passenger domains (51).…”

Autotransporter proteins of Uropathogenic Escherichia coli: regulation, characterisation and the role of periplasmic proteins in their expression

“…UpaG have also shown to promote cell-cell auto-aggregation, contribute to biofilm formation and mediate adherence to eukaryotic cells (Valle et al, 2008a, Leo et al, 2011 (Oberhettinger et al, 2012). Intimin is produced by EPEC and EHEC strains and contributes to the formation of characteristic attachment and effacing lesions associated with these pathogens (Jerse et al, 1990, Donnenberg et al, 1993.…”