Uncoupling of GTP Binding from Target Stimulation by a Single Mutation in the Transducin α Subunit

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Science  08 Mar 1996:
Vol. 271, Issue 5254, pp. 1413-1416
DOI: 10.1126/science.271.5254.1413


Glutamic acid-203 of the alpha subunit of transducin (αT) resides within a domain that undergoes a guanosine triphosphate (GTP)-induced conformational change that is essential for effector recognition. Changing the glutamic acid to an alanine in bovine αT yielded an alpha subunit (αTE203A) that was fully dependent on rhodopsin for GTP-guanosine diphosphate (GDP) exchange and showed GTP hydrolytic activity similar to that measured for wild-type αT. However, unlike the wild-type protein, the GDP-bound form of αTE203A was constitutively active toward the effector of transducin, the cyclic guanosine monophosphate phosphodiesterase. Thus, the αTE203A mutant represents a short-circuited protein switch that no longer requires GTP for the activation of the effector target phosphodiesterase.