Over the past decade C. difficile has become a global epidemic causing life-threatening diarrhea with massive outbreaks in hospitals in the U.S., Canada and Europe. In its 2013 report the CDC has classified this pathogen as an urgent antibiotic-resistance threat. It causes half a million infections per year in the U.S. alone requiring hospitalization (costs about 1 Bn USD) with about 29,000 associated deaths . C. difficile Zmp1 is a secreted metalloprotease related to the Lethal Factor from B. anthracis. It is implied as potential virulence factor related to cell motility. It possesses a unique specificity for Pro-Pro peptide bonds. For virtually all types of proteases this kind of peptide bond is very difficult to cleave. For the first time we have determined high-resolution crystal structures of Zmp1 in the unbound and substrate- and product-bound states, thus shedding light on its unique sequence specificity. These crystal structures reveal open and closed conformations of the large S-loop and shed light on the binding mode of the substrate. A number of unique structural features are present and help to explain the unique substrate specificity. The peptide-bound structures reveal important residues for substrate recognition and the strict specificity of Zmp1 for Pro-Pro peptide bonds.This structural information will also be useful in the rational design of inhibitors that may be useful in antibiotic-supporting therapeutic approaches.
References:
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