The Corynebacterium diphtheriae shaft pilin SpaA is built of tandem lg-like modules with stabilizing isopeptide and disulfide bonds

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 40; p. 16967
• Main Authors: Kang, Hae Joo, Paterson, Neil G, Gaspar, Andrew H, Ton-That, Hung, Baker, Edward N
• Format: Journal Article
• Language: English
• Published: Washington National Academy of Sciences 06.10.2009
• Subjects: Cells; Crystal structure; Genetics; Gram-positive bacteria; Molecular structure; Peptides; Proteins
• ISSN: 0027-8424; 1091-6490

Cell-surface pili are important virulence factors that enable bacterial pathogens to adhere to specific host tissues and modulate host immune response. Relatively little is known about the structure of Gram-positive bacterial pili, which are built by the sortase-catalyzed covalent crosslinking of individual pilin proteins. Here we report the 1.6-A resolution crystal structure of the shaft pilin component SpaA from Corynebacterium diphtheriae, revealing both common and unique features. The SpaA pilin comprises 3 tandem Ig-like domains, with characteristic folds related to those typically found in non-pilus adhesins. Whereas both the middle and the C-terminal domains contain an intramolecular Lys-Asn isopeptide bond, previously detected in the shaft pilins of Streptococcus pyogenes and Bacillus cereus, the middle Ig-like domain also harbors a calcium ion, and the C-terminal domain contains a disulfide bond. By mass spectrometry, we show that the SpaA monomers are cross-linked in the assembled pili by a Lys-Thr isopeptide bond, as predicted by previous genetic studies. Together, our results reveal that despite profound dissimilarities in primary sequences, the shaft pilins of Gram-positive pathogens have strikingly similar tertiary structures, suggesting a modular backbone construction, including stabilizing intermolecular and intramolecular isopeptide bonds. [PUBLICATION ABSTRACT]