title: Structural basis for group B streptococcus pilus 1 sortases C regulation and specificity.
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.
authors.affiliation: Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Cozzi
authors.forename: Daniil
authors.initials: D
authors.lastname: Prigozhin
authors.forename: Roberto
authors.initials: R
authors.lastname: Rosini
authors.forename: Francesca
authors.initials: F
authors.lastname: Abate
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Bottomley
authors.forename: Guido
authors.initials: G
authors.lastname: Grandi
authors.forename: John L
authors.initials: JL
authors.lastname: Telford
authors.forename: C Daniela
authors.initials: CD
authors.lastname: Rinaudo
authors.forename: Domenico
authors.initials: D
authors.lastname: Maione
authors.forename: Tom
authors.initials: T
authors.lastname: Alber
mesh_terms: D019881:Aminoacyltransferases / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray / Q000379:methods; D003546:Cysteine Endopeptidases / Q000737:chemistry*; D036781:Fimbriae Proteins / Q000737:chemistry*; D010861:Fimbriae, Bacterial / Q000737:chemistry*; D008958:Models, Molecular; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013291:Streptococcus / Q000737:chemistry / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; C509822:sortase C; D036781:Fimbriae Proteins; D019881:Aminoacyltransferases; D003546:Cysteine Endopeptidases