ABSTRACT
Recent studies have shown that cholesterol plays a significant role in the ability of Toxin A from Clostridium difficile to enter eukaryotic cells. The translocation process is one of three major steps during intoxication that could be targeted for intervention against the severe antibiotic-associated diarrhea caused by C. difficile.
Subject(s)
Clostridioides difficile/metabolism , Enterocolitis, Pseudomembranous/epidemiology , Opportunistic Infections/microbiology , Bacterial Proteins/chemistry , Bacterial Proteins/pharmacokinetics , Bacterial Proteins/toxicity , Bacterial Toxins/chemistry , Bacterial Toxins/pharmacokinetics , Bacterial Toxins/toxicity , Cholesterol/deficiency , Clostridioides difficile/pathogenicity , Cross Infection/epidemiology , Cross Infection/prevention & control , Diarrhea/microbiology , Enterotoxins/chemistry , Enterotoxins/pharmacokinetics , Enterotoxins/toxicity , Humans , Membrane Lipids/physiologyABSTRACT
Uridine-5'-diphospho-1-alpha-d-glucose (UDP-Glc) is a common substrate used by glucosyltransferases, including certain bacterial toxins such as Toxins A and B from Clostridium difficile. Fluorescent analogs of UDP-Glc have been prepared for use in our studies of the clostridial toxins. These compounds are related to the methylanthraniloyl-ATP compounds commonly used to probe the chemistry of ATP-dependent enzymes. The reaction of excess methylisatoic anhydride with UDP-Glc in aqueous solution yields primarily the 2' and 3' isomers of methylanthraniloyl-UDP-Glc (MUG). As the 2' and 3' isomers readily interconvert, this isomeric mixture was copurified by HPLC away from the other isomeric products, and was characterized by a combination of NMR, fluorescence and mass spectrometric methods. TcdA binds MUG competitively with respect to UDP-Glc with an affinity of 15 +/- 2 microm in the absence of Mg2+. There is currently no evidence that the fluorescent substrate analog is turned over by the toxin in either glucosyltransferase or glucosylhydrolase reactions. Using a competition assay, the affinity of UDP-Glc was determined to be 45+/-10 microm in the absence of Mg2+. The binding of UDP-Glc and Mg2+ are highly coupled with Mg2+ affinities in the range of 90-600 microm, depending on the experimental conditions. These results imply that one of the significant roles of the metal ion might be to stabilize the enzyme-substrate complex prior to initiation of the transferase chemistry.