Expression, purification, crystallization and preliminary crystallographic analysis of a putative Clostridium difficile surface protein Cwp19

Cwp19 Is a Novel Lytic Transglycosylase Involved in Stationary-Phase Autolysis Resulting in Toxin Release in Clostridium difficile

Clostridium difficile is the major etiologic agent of antibiotic-associated intestinal disease. Pathogenesis of C. difficile is mainly attributed to the production and secretion of toxins A and B. Unlike most clostridial toxins, toxins A and B have no signal peptide, and they are therefore secreted by unusual mechanisms involving the holin-like TcdE protein and/or autolysis. In this study, we characterized the cell surface protein Cwp19, a newly identified peptidoglycan-degrading enzyme containing a novel catalytic domain. We purified a recombinant His₆-tagged Cwp19 protein and showed that it has lytic transglycosylase activity. Moreover, we observed that Cwp19 is involved in cell autolysis and that a C. difficilecwp19 mutant exhibited delayed autolysis in stationary phase compared to the wild type when bacteria were grown in brain heart infusion (BHI) medium. Wild-type cell autolysis is correlated to strong alterations of cell wall thickness and integrity and to release of cytoplasmic material. Furthermore, we demonstrated that toxins were released into the extracellular medium as a result of Cwp19-induced autolysis when cells were grown in BHI medium. In contrast, Cwp19 did not induce autolysis or toxin release when cells were grown in tryptone-yeast extract (TY) medium. These data provide evidence for the first time that TcdE and bacteriolysis are coexisting mechanisms for toxin release, with their relative contributions in vitro depending on growth conditions. Thus, Cwp19 is an important surface protein involved in autolysis of vegetative cells of C. difficile that mediates the release of the toxins from the cell cytosol in response to specific environment conditions.IMPORTANCEClostridium difficile-associated disease is mainly known as a health care-associated infection. It represents the most problematic hospital-acquired infection in North America and Europe and exerts significant economic pressure on health care systems. Virulent strains of C. difficile generally produce two toxins that have been identified as the major virulence factors. The mechanism for release of these toxins from bacterial cells is not yet fully understood but is thought to be partly mediated by bacteriolysis. Here we identify a novel peptidoglycan hydrolase in C. difficile, Cwp19, exhibiting lytic transglycosylase activity. We show that Cwp19 contributes to C. difficile cell autolysis in the stationary phase and, consequently, to toxin release, most probably as a response to environmental conditions such as nutritional signals. These data highlight that Cwp19 constitutes a promising target for the development of new preventive and curative strategies.

The molecular structure of the glycoside hydrolase domain of Cwp19 from Clostridium difficile

Clostridium difficile is a burden to healthcare systems around the world, causing tens of thousands of deaths annually. The S‐layer of the bacterium, a layer of protein found of the surface of cells, has received a significant amount of attention over the past two decades as a potential target to combat the growing threat presented by C. difficile infections. The S‐layer contains a wide range of proteins, each of which possesses three cell wall‐binding domains, while many also possess a “functional” region. Here, we present the high resolution structure of the functional region of one such protein, Cwp19 along with preliminary functional characterisation of the predicted glycoside hydrolase. Cwp19 has a TIM barrel fold and appears to possess a high degree of substrate selectivity. The protein also exhibits peptidoglycan hydrolase activity, an order of magnitude slower than that of lysozyme and is the first member of glycoside hydrolase‐like family 10 to be characterised. This research goes some way to understanding the role of Cwp19 in the S‐layer of C. difficile.

Database

Structural data are available in the PDB under the accession numbers 5OQ2 and 5OQ3.