ADP-ribosylation by cholera toxin: functional analysis of a cellular system that stimulates the enzymic activity of cholera toxin fragment A1. Biochemistry 1987 Oct 06;26(20):6364-71
Date
10/06/1987Pubmed ID
3322378DOI
10.1021/bi00394a009Scopus ID
2-s2.0-0023646687 (requires institutional sign-in at Scopus site) 42 CitationsAbstract
We have clarified relationships between cholera toxin, cholera toxin substrates, a membrane protein S that is required for toxin activity, and a soluble protein CF that is needed for the function of S. The toxin has little intrinsic ability to catalyze ADP-ribosylations unless it encounters the active form of the S protein, which is S liganded to GTP or to a GTP analogue. In the presence of CF, S.GTP forms readily, though reversibly, but a more permanent active species, S-guanosine 5'-O-(3-thiotriphosphate) (S.GTP gamma S), forms over a period of 10-15 min at 37 degrees C. Both guanosine 5'-O-(2-thiodiphosphate) and GTP block this quasi-permanent activation. Some S.GTP gamma S forms in membranes that are exposed to CF alone and then to GTP gamma S, with a wash in between, and it is possible that CF facilitates a G nucleotide exchange. S.GTP gamma S dissolved by nonionic detergents persists in solution and can be used to support the ADP-ribosylation of nucleotide-free substrates. In this circumstance, added guanyl nucleotides have no further effect. This active form of S is unstable, especially when heated, but the thermal inactivation above 45 degrees C is decreased by GTP gamma S. Active S is required equally for the ADP-ribosylation of all of cholera toxin's protein substrates, regardless of whether they bind GTP or not. We suggest that active S interacts directly with the enzymic A1 fragment of cholera toxin and not with any toxin substrate.(ABSTRACT TRUNCATED AT 250 WORDS)
Author List
Gill DM, Coburn JAuthor
Jenifer Coburn PhD Professor in the Medicine department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Adenosine Diphosphate RiboseAnimals
Cattle
Cholera Toxin
Erythrocyte Membrane
Guanosine 5'-O-(3-Thiotriphosphate)
Guanosine Triphosphate
Kinetics
Male
Peptide Fragments
Proteins
Testis
Thionucleotides