Structural Basis for Group B Streptococcus Pilus 1 Sortases C Regulation and Specificity |
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Authors: | Roberta Cozzi Daniil Prigozhin Roberto Rosini Francesca Abate Matthew J. Bottomley Guido Grandi John L. Telford C. Daniela Rinaudo Domenico Maione Tom Alber |
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Affiliation: | 1. Novartis Vaccines and Diagnostics, Siena, Italy.; 2. University of California, Berkeley, United States of America.; University of Kansas Medical Center, United States of America, |
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Abstract: | Gram-positive bacteria assemble pili through class C sortase enzymes specialized in polymerizing pilin subunits into covalently linked, high-molecular-weight, elongated structures. Here we report the crystal structures of two class C sortases (SrtC1 and SrtC2) from Group B Streptococcus (GBS) Pilus Island 1. The structures show that both sortases are comprised of two domains: an 8-stranded β-barrel catalytic core conserved among all sortase family members and a flexible N-terminal region made of two α-helices followed by a loop, known as the lid, which acts as a pseudo-substrate. In vitro experiments performed with recombinant SrtC enzymes lacking the N-terminal portion demonstrate that this region of the enzyme is dispensable for catalysis but may have key roles in substrate specificity and regulation. Moreover, in vitro FRET-based assays show that the LPXTG motif common to many sortase substrates is not the sole determinant of sortase C specificity during pilin protein recognition. |
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