ADP-ribosylation of bovine S-antigen by cholera toxin |
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Authors: | N Komori M A Rider D J Takemoto H Shichi H Matsumoto |
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Affiliation: | Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City 73190. |
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Abstract: | The S-antigen (alias 48K protein or arrestin) of bovine rod photoreceptors contains two stretches of amino acid sequence homologous to the ADP-ribosylation sites of the alpha subunit of transducin (Ta). We have found that cholera toxin transfers the ADP-ribosyl group from NAD to purified bovine S-antigen as well as to S-antigen in rod outer segment membranes, while Bordetella pertussis toxin is unable to catalyze the transfer reaction efficiently. Under the same conditions, both toxins catalyzed ADP-ribosylation of Ta in rod outer segments. The ADP-ribosylation of S-antigen by cholera toxin indicates that S-antigen not only exhibits sequence homology with the ADP-ribosylation sites of Ta, but it must also resemble Ta in the tertiary structure of the domain which determines the susceptibility of S-antigen to the catalytic action of cholera toxin. These results suggest that S-antigen may function as a competitor of Ta in some stage of the cGMP cascade of visual transduction. |
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