Alternative folding to a monomer or homopolymer is a common feature of the type 1 pilus subunit FimA from enteroinvasive bacteria

Open access
Date
2019-07-05Type
- Journal Article
Abstract
Adhesive type 1 pili from enteroinvasive, Gram-negative bacteria mediate attachment to host cells. Up to 3000 copies of the main pilus subunit, FimA, assemble into the filamentous, helical quaternary structure of the pilus rod via a mechanism termed donor-strand complementation, in which the N-terminal extension of each subunit, the donor strand, is inserted into the incomplete immunoglobulin-like fold of the preceding FimA subunit. For FimA from Escherichia coli, it has been previously shown that the protein can also adopt a monomeric, self-complemented conformation in which the donor strand is inserted intramolecularly in the opposite orientation relative to that observed for FimA polymers. Notably, soluble FimA monomers can act as apoptosis inhibitors in epithelial cells after uptake of type 1-piliated pathogens. Here, we show that the FimA orthologues from Escherichia coli, Shigella flexneri, and Salmonella enterica can all fold to form self-complemented monomers. We solved X-ray structures of all three FimA monomers at 0.89–1.69 Å resolutions, revealing identical, intramolecular donor-strand complementation mechanisms. Our results also showed that the pseudo-palindromic sequences of the donor strands in all FimA proteins permit their alternative folding possibilities. All FimA monomers proved to be 50–60 kJ/mol less stable against unfolding than their pilus rod-like counterparts (which exhibited very high energy barriers of unfolding and refolding). We conclude that the ability of FimA to adopt an alternative, monomeric state with anti-apoptotic activity is a general feature of FimA proteins of type 1-piliated bacteria. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000358944Publication status
publishedExternal links
Journal / series
Journal of Biological ChemistryVolume
Pages / Article No.
Publisher
American Society for Biochemistry and Molecular BiologySubject
protein folding; X-ray crystallography; Escherichia coli (E; coli); protein structure; protein stability; alternative folding; chaperone-usher pili; FimA; type 1 pilus; urinary tract infectionsOrganisational unit
03412 - Glockshuber, Rudolf (emeritus) / Glockshuber, Rudolf (emeritus)
Funding
176403 - Mechanism of assembly and receptor binding of adhesive pili from pathogenic bacteria (SNF)
156304 - Functional significance of the dynamics of receptor binding and the alternative folding possibilities of pilus subunits in urinary tract infections caused by pathogenic Escherichia coli strains (SNF)
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