Metagenomic Search Reveals S. Enterica Protein with Structural Similarity to C. Difficile Toxin A

Abstract

Clostridioides difficile infection (CDI) causes thousands of deaths a year in the United States. The symptoms of CDI are shown to be primarily attributed to the glycosyltransferase activity of toxin A (TcdA) and toxin B (TcdB). While this mechanism is well-characterized in C. difficile, similar glycosyltransferases in non-Clostridioides species remain largely unstudied. This study hypothesized that proteins with sequence and structural similarity to the glycosyltransferase domain (GTD) of TcdA may be present across bacterial genera. Using metagenomic database search, several proteins with sequence similarity to TcdA’s GTD across several species were identified. Further analysis of a GT44 domain-containing protein in Salmonella enterica (GT44_Se) showed limited sequence and structural homology to TcdA. Multiple sequence alignment across proteins from a variety of species revealed conservation of key residues within the GTD-associated region. These findings identify computational candidate bacterial proteins with limited sequence and predicted structural similarity to TcdA GTD that warrant experimental characterization. However, the computational analyses performed in this study do not establish glycosyltransferase activity, toxin function, or a role in virulence. Further biochemical studies are necessary to determine if the potential proteins are functional homologs to TcdA’s GTD.