Donor-strand exchange in chaperone-assisted pilus assembly proceeds through a concerted beta strand displacement mechanism.

TitleDonor-strand exchange in chaperone-assisted pilus assembly proceeds through a concerted beta strand displacement mechanism.
Publication TypeJournal Article
Year of Publication2006
AuthorsRemaut, H., R. J. Rose, T. J. Hannan, S. J. Hultgren, S. E. Radford, A. E. Ashcroft, and G. Waksman
JournalMol Cell
Volume22
Issue6
Pagination831-42
Date Published2006 Jun 23
Type of Articlesmm
ISSN1097-2765
KeywordsBacterial Proteins, Crystallography, X-Ray, Fimbriae, Bacterial, Models, Molecular, Molecular Chaperones, Multiprotein Complexes, Protein Folding, Protein Structure, Secondary, Protein Structure, Tertiary, Salmonella enterica, Spectrometry, Mass, Electrospray Ionization
Abstract

Gram-negative pathogens commonly use the chaperone-usher pathway to assemble adhesive multisubunit fibers on their surface. In the periplasm, subunits are stabilized by a chaperone that donates a beta strand to complement the subunits' truncated immunoglobulin-like fold. Pilus assembly proceeds through a "donor-strand exchange" (DSE) mechanism whereby this complementary beta strand is replaced by the N-terminal extension (Nte) of an incoming pilus subunit. Using X-ray crystallography and real-time electrospray ionization mass spectrometry (ESI-MS), we demonstrate that DSE requires the formation of a transient ternary complex between the chaperone-subunit complex and the Nte of the next subunit to be assembled. The process is crucially dependent on an initiation site (the P5 pocket) needed to recruit the incoming Nte. The data also suggest a capping reaction displacing DSE toward product formation. These results support a zip-in-zip-out mechanism for DSE and a catalytic role for the usher, the molecular platform at which pili are assembled.

DOI10.1016/j.molcel.2006.05.033
Alternate JournalMol. Cell
PubMed ID16793551