Covalent attachment and Pro‐Pro endopeptidase (PPEP‐1)‐mediated release of Clostridium difficile cell surface proteins involved in adhesion

Abstract

In the past decade, Clostridium difficile has emerged as an important gut pathogen. This anaerobic, Gram-positive bacterium is the main cause of infectious nosocomial diarrhea. Whereas much is known about the mechanism through which the C. difficile toxins cause diarrhea, relatively little is known about the dynamics of adhesion and motility, which is mediated by cell surface proteins. This review will discuss the recent advances in our understanding of the sortase-mediated covalent attachment of cell surface (adhesion) proteins to the peptidoglycan layer of C. difficile and their release through the action of a highly specific secreted metalloprotease (Pro-Pro endopeptidase 1, PPEP-1). Specific emphasis will be on a model in which PPEP-1 and its substrates control the switch from a sessile to motile phenotype in C. difficile, and how this is regulated by the cyclic dinucleotide c-di-GMP (3'-5' cyclic dimeric guanosine monophosphate).

Dual role of the colonization factor CD2831 in Clostridium difficile pathogenesis

“…CD2831 and another c-di-GMP controlled putative adhesin, CD3246, are recognized and cleaved by ZmpI/PPEP-1. Consistently, it was demonstrated that at low c-di-GMP levels, ZmpI/PPEP-1 is produced and cleaves the low amount of CD2831 and CD3246 present, thus limiting bacterial adhesion to the host 44–46 .…”

Cyclic diguanylate riboswitches control bacterial pathogenesis mechanisms

“…The zmpI mRNA (CD630_28300) contains a class I riboswitch and is negatively regulated by c-di-GMP. The opposing regulation of ZmpI and its surface protein targets has been proposed to integrate increased c-di-GMP to simultaneously promote production of the surface proteins and inhibit their release by ZmpI [36]. Together these studies indicate that, as in other bacterial species, C .…”

Discovery of a new Pro-Pro endopeptidase, PPEP-2, provides mechanistic insights into the differences in substrate specificity within the PPEP family

“…The gene encoding PPEP-1 in C. difficile (ppep-1/cd2830) is found adjacent to cd2831, the gene that encodes its substrate (21,22). In CD2831, multiple PPEP-1 cleavage sites are present, located just above the site of attachment to the peptidoglycan layer.…”

“…We have recently characterized a novel secreted protease in Clostridium difficile, Pro-Pro endopeptidase (PPEP 3 -1, 3.4.24.89, previously known as Zmp1 (19) (MER0494994)), which has a remarkable preference for hydrolyzing a Pro-Pro bond (20,21). PPEP-1 cleaves two cell C. difficile surface adhesion proteins (CD2831 and CD3246) and as such is thought to play a role in switching from an adhesive to a motile phenotype (22). The two substrates of PPEP-1 contain multiple consecutive cleavage sites (in total 13), and a consensus motif analysis showed that in addition to the prolines surrounding the scissile bond, highly conserved residues are found, and cleavage preferentially occurs at sites that are composed of (VLI)NPPVP (P3-P3Ј).…”