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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 PMID: 3322378

Pubmed ID

3322378

Abstract

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 J

Author

Jenifer Coburn PhD Professor in the Medicine department at Medical College of Wisconsin




Scopus

2-s2.0-0023646687   35 Citations

MESH terms used to index this publication - Major topics in bold

Adenosine Diphosphate Ribose
Animals
Cattle
Cholera Toxin
Erythrocyte Membrane
Guanosine 5'-O-(3-Thiotriphosphate)
Guanosine Triphosphate
Kinetics
Male
Peptide Fragments
Proteins
Testis
Thionucleotides
jenkins-FCD Prod-331 a335b1a6d1e9c32173c9534e6f6ff51494143916