Abstract
Zymography is a widely used technique enabling visualization of in-gel peptidase/protease hydrolytic activities. This technique is used to study the activity of bacterial peptidoglycan (PG) hydrolytic enzymes named autolysins. Zymography is particularly suited for PG autolysin characterization as bulk PG is notorious to work with due to its highly insoluble nature. This recalcitrant property of PG therefore makes the setup of PG hydrolytic activity assay very challenging. In the course of studying the catalytic activity of the CwlS protein, a D,L NlpC/P60 endopeptidase possessing multiple LysM carbohydrate binding-domains from Bacillus subtilis, we observed a potential artifact of the zymography technique. The generation of CwlS truncated mutants impaired in their PG binding capacity presented lower apparent hydrolytic activities on zymograms. Furthermore, a catalytically dead version of CwlS, or a CwlS mutant that possesses only its LysM domains and no catalytic domain, maintained similar apparent PG hydrolytic properties as wild-type CwlS on zymograms. Additionally, a mutant harboring twelve mutations in the four LysM domains, previously demonstrated to be unable to bind PG but has a similar net positive charge as the wild-type protein presents also apparent activity on zymogram. We demonstrate in this study that zymography results, which are meant to be interpreted in favor of apparent PG hydrolytic activities, are instead reflecting impairment of gel staining probably due to the very high net positive charge of the protein. Opposed Reviewers: Abstract Zymography is a widely used technique enabling visualization of in-gel