Predicted C. difficile SrtB secondary structure . A structural alignment between the known crystal structure of BaSrtB  and the predicted structure of C. difficile SrtB using the Phyre2 Protein Fold Recognition Server suggests a high degree of structural conservation. Top: C. difficile SrtB predicted secondary structure and sequence. Bottom: BaSrtB sequence and known structure. Arrows indicate beta sheets, and striped rectangles indicate alpha helixes. Amino acid positions relative to start position are indicated. The sortase active site signature sequence TLXTC is boxed, as are the conserved essential histidine and arginine residues.