Effects of temperature on ADP-ribosylation factor stimulation of cholera toxin activity.
The effects of cholera toxin, a secretory product of Vibrio cholerae, result from ADP-ribosylation of the stimulatory guanine nucleotide-binding (Gs) protein of the adenylyl cyclase system. Cholera toxin A subunit (CTA) also uses agmatine, a simple guanidino compound, several proteins unrelated to Gs, and CTA itself as alternative ADP-ribose acceptors. The effects of toxin occur in the jejunum presumably at body core temperature. With agmatine as a model substrate, the optimal temperature for CTA-catalyzed ADP-ribosylation was 25-30 degrees C, and that for CTA-catalyzed auto-ADP-ribosylation was 20-25 degrees C. Both activities were significantly less at 37 degrees C, reflecting lower initial velocities, not heat-inactivation of the toxin. All the transferase activities of CTA are enhanced by ADP-ribosylation factors (ARFs), approximately 20-kDa guanine nucleotide-binding proteins that are ubiquitous in mammalian cells. Phospholipids and a soluble brain ARF, in a GTP-dependent manner, activated toxin NAD:agmatine ADP-ribosyltransferase activity; their simultaneous effect was maximal at physiological temperatures (approximately 37 degrees C). At lower temperatures, the stimulation by ARF was much less. There were similar effects on other toxin-catalyzed reactions, notably, the ADP-ribosylation of Gs alpha and the hydrolysis of NAD. Thus, host factors, such as ARF and phospholipid, synergistically increase cholera toxin activity at 37 degrees C and may be important in toxin action in the mammalian gut.
Murayama
T
T
Laboratory of Cellular Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
Tsai
S C
SC
Adamik
R
R
Moss
J
J
Vaughan
M
M
D020727:ADP-Ribosylation Factors; D000376:Agmatine / Q000378:metabolism; D000494:Allosteric Regulation; D000818:Animals; D002308:Cardiolipins / Q000494:pharmacology; D002417:Cattle; D002772:Cholera Toxin / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology; D011817:Rabbits; D013379:Substrate Specificity; D013696:Temperature
D002308:Cardiolipins; D003902:Detergents; D006150:Guanine Nucleotides; D010743:Phospholipids; D000376:Agmatine; D002772:Cholera Toxin; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors