The Corynebacterium diphtheriae shaft pilin SpaA is built of tandem Ig-like modules with stabilizing isopeptide and disulfide bonds.
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.
Kang
Hae Joo
HJ
Maurice Wilkins Centre for Molecular Biodiscovery and School of Biological Sciences, University of Auckland, Auckland 1020, New Zealand.
Paterson
Neil G
NG
Gaspar
Andrew H
AH
Ton-That
Hung
H
Baker
Edward N
EN
D000595:Amino Acid Sequence; D001216:Asparagine / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003353:Corynebacterium diphtheriae / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D036781:Fimbriae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007136:Immunoglobulins / Q000737:chemistry / Q000378:metabolism; D008239:Lysine / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013912:Threonine / Q000737:chemistry / Q000378:metabolism
D001426:Bacterial Proteins; D004220:Disulfides; D007136:Immunoglobulins; D036781:Fimbriae Proteins; D013912:Threonine; D001216:Asparagine; D008239:Lysine