Link to Pubmed [PMID] – 26283789
J. Biol. Chem. 2015 Aug;
In Gram-positive pathogens, surface proteins may be covalently anchored to the bacterial peptidoglycan by sortase, a cysteine transpeptidase enzyme. In contrast to other Gram-positive bacteria, only one single sortase enzyme, SrtB, is conserved between strains of Clostridium difficile. Sortase-mediated peptidase activity has been reported in vitro and seven potential substrates have been identified. Here we demonstrate the functionality of sortase in C. difficile. We identify two sortase-anchored proteins, the putative adhesins CD2831 and CD3246, and determine the cell wall anchor structure of CD2831. The C-terminal PPKTG sorting motif of CD2831 is cleaved between the threonine and glycine residues and the carboxyl group of threonine is amide-linked to the side chain amino group of diaminopimelic acid within the peptidoglycan peptide stem. We show that CD2831 protein levels are elevated in presence of high intracellular cyclic di-GMP (c-di-GMP) concentrations, in agreement with the control of CD2831 expression by a c-di-GMP-dependent type II riboswitch. Low c-di-GMP levels induce the release of CD2831, and presumably CD3246, from the surface of cells. This regulation is mediated by proteolytic cleavage of CD2831 and CD3246 by the zinc metalloprotease ZmpI, whose expression is controlled by a type II c-di-GMP riboswitch. These data reveal a novel regulatory mechanism for expression of two sortase substrates by the secondary messenger c-di-GMP, on which surface anchoring is dependent.