Background Bacterial sortases are transpeptidases that covalently anchor surface proteins to the peptidoglycan of the Gram-positive cell wall. (S/P)PXTG peptide. Small-molecule inhibitors recognized through an screen inhibit SrtB enzymatic activity to a greater degree than MTSET. Conclusions Dabigatran These results demonstrate for the first time that encodes a single Dabigatran sortase enzyme, which cleaves motifs made up of (S/P)PXTG Sortase A (SaSrtA), are considered housekeeping sortases as they are capable of anchoring many functionally unique proteins to the cell wall. SaSrtA, which recognizes an LPXTG motif, is responsible for anchoring a variety of surface proteins involved in adherence and immune response evasion, and is essential for virulence in animal models [8,9]. SrtA orthologues Dabigatran have been found in the genomes of almost all Gram-positive bacteria [8,10C16]. Class B sortases are functionally different from class A in their substrate specificity. In and (iron-responsive surface determinant) responsible for heme-iron transport, and anchors the iron transporter protein, IsdC, by realizing an NPQTN motif [17,18]. Though mutating has no effect on establishing contamination, SaSrtB is required for persistence of the bacterium in mice . can result in a SF3a60 range of clinical presentations, from mild self-limiting diarrhea to the life-threatening Dabigatran pseudomembranous colitis (PMC), known collectively as infection (CDI) . MLST studies have identified that the population structure forms at least five distinct lineages that are all associated with CDI [20C22]. Complications of severe CDI can lead to toxic megacolon, bowel perforation, sepsis and death in up to 25% of cases . Broad-spectrum antibiotic usage is the greatest risk factor for development of CDI due to the consequent disruption of the intestinal microflora. Treatment of CDI with metronidazole and vancomycin can exacerbate the problem by continuing to disrupt the intestinal microflora. This leaves the patient susceptible to relapse or re-infection. Approximately one third of patients experience CDI relapse following treatment, and those who relapse have a greater risk of succumbing to the infection . A current imperative is the development of therapies that selectively target reference strain 630 encodes a single predicted sortase, CD630_27180, which has high amino-acid similarity with SrtB of and . A second Dabigatran sortase encoded within the genome is interrupted by a stop codon prior to the catalytic cysteine and is considered a pseudogene. Thus, in contrast to other Gram-positive bacteria, appears to have only a single functional sortase. As such, a compound that inhibits the activity of sortase could target the pathogen without disrupting the numerous Gram-negative bacteria that make up the intestinal flora. In this study, we demonstrate that the predicted sortase encoded by CD630_27180 recognizes and cleaves an (S/P)PXTG motif between the threonine and glycine residues. The cleavage of this motif is dependent on the conserved cysteine residue at position 209 in the predicted active site of the sortase. We have also identified seven putative sortase substrates, all of which contain the (S/P)PXTG motif. These substrates are conserved among the five lineages and include potential adhesins, a 5 nucleotidase, and cell wall hydrolases. Furthermore, we identified a number of small-molecule inhibitors by means of an screen that inhibit the activity of the SrtB. Results Conservation of the catalytically active residues of sortase The genome sequence of strain 630 previously indicated the presence of a single copy of a sortase-like protein, encoded by shares 32% and 34% amino acid identity with SrtB from (SaSrtB) and (BaSrtB), respectively. In addition to the TLXTC active site, the catalytically essential histidine (His120 in SaSrtA) and arginine (R197 in SaSrtA) residues [3,25,26] are conserved in the SrtB. A structural prediction analysis of SrtB was performed using Phyre2 Protein Fold Recognition Server (http://www.sbg.bio.ic.ac.uk/phyre2/html/page.cgi?id=index) , and the resulting alignment.