ADP-ribosylation by cholera toxin: functional analysis of a cellular system that stimulates the enzymic activity of cholera toxin fragment A/sub 1/

Journal Article · Tue Oct 06 00:00:00 EDT 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00394a009· OSTI ID:5515367

Gill, D M; Coburn, J

The authors 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 x GTP forms readily, though reversibly, but a more permanent active species, S-guanosine 5'-O-(3-thiotriphosphate) (S x GTP..gamma..S), forms over a period of 10-15 min at 37/sup 0/C. Both guanosine 5'-O-(2-thiodiphosphate) and GTP block this quasi-permanent activation. Some S x 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 x 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/sup 0/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. They suggest that active S interacts directly with the enzymic A/sub 1/ fragments of cholera toxin and not with any toxin substrate. The activation and activity of S are independent of the state, or even the presence, of adenylate cyclase and seem to be involved with the cyclase system only via cholera toxin. S is apparently not related by function to certain other GTP binding proteins, including p21/sup ras/, and appears to be a new GTP binding protein whose physiologic role remains to be identified.

• Research Organization: Tufts Univ., Boston, MA
• OSTI ID: 5515367
• Journal Information: Biochemistry; (United States), Vol. 26:20
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
PROTEINS
BIOCHEMISTRY
TOXINS
CHEMICAL ACTIVATION
ADP
BIRDS
CELL MEMBRANES
CHOLERA
ENZYME ACTIVITY
ERYTHROCYTES
LABELLED COMPOUNDS
NUCLEOTIDES
PHOSPHORUS 32
PHYSIOLOGY
SUBSTRATES
ANIMALS
ANTIGENS
BACTERIAL DISEASES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BODY FLUIDS
CELL CONSTITUENTS
CHEMISTRY
DAYS LIVING RADIOISOTOPES
DISEASES
INFECTIOUS DISEASES
ISOTOPES
LIGHT NUCLEI
MATERIALS
MEMBRANES
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHOSPHORUS ISOTOPES
RADIOISOTOPES
TOXIC MATERIALS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques