Intestinal bile acids directly modulate the structure and function of <i>C. difficile</i> TcdB toxin

Abstract

Intestinal bile acids are known to modulate the germination and growth of <i>Clostridioides difficile</i> Here we describe a role for intestinal bile acids in directly binding and neutralizing TcdB toxin, the primary determinant of <i>C. difficile</i> disease. We show that individual primary and secondary bile acids reversibly bind and inhibit TcdB to varying degrees through a mechanism that requires the combined oligopeptide repeats region to which no function has previously been ascribed. We find that bile acids induce TcdB into a compact "balled up" conformation that is no longer able to bind cell surface receptors. Lastly, through a high-throughput screen designed to identify bile acid mimetics we uncovered nonsteroidal small molecule scaffolds that bind and inhibit TcdB through a bile acid-like mechanism. In addition to suggesting a role for bile acids in <i>C. difficile</i> pathogenesis, these findings provide a framework for development of a mechanistic class of <i>C. difficile</i> antitoxins.