Dual role of the colonization factor CD2831 in C. difficile pathogenesis

Clostridium difficile is a Gram-positive, anaerobic bacterium and the leading cause of antibiotic- associated diarrhea and pseudomembranous colitis. C. difficile modulates the transition from a motile to a sessile lifestyle through a mechanism of riboswitches regulated by cyclic diguanosine monophosphate (c-di-GMP). Previously described as positively regulated by c-di-GMP, CD2831 was annotated as putative collagen-binding protein and thus potentially involved in sessility. CD2831 is a Sortase substrate and it belongs to the Microbial Surface Components Recognizing Adhesive Matrix Molecule (MSCRAMMs) family, a class of virulence factors that has been recently reported to play a role also in host immune evasion by binding to human complement components. With the overexpression of CD2831 in C. difficile and the heterologous expression on Lactococcus lactis surface, here we show that CD2831 is a collagen-binding protein, able to bind to immobilized collagen types I, III and V and to the collagen produced by human fibroblasts. We also observed that the overexpression of CD2831 increases the ability to form biofilm on abiotic surface in both C. difficile and L. lactis. Notably, similarly to other MSCRAMMs, we showed that CD2831 binds to the collagen-like domain of the human complement C1q, preventing the C1 complex formation and the activation of the complement cascade via classical pathway