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

Publisher Website
Google Scholar
Abstract
Glutamic acid-203 of the alpha subunit of transducin (α T ) 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 α T yielded an alpha subunit (α T E203A) that was fully dependent on rhodopsin for GTP-guanosine diphosphate (GDP) exchange and showed GTP hydrolytic activity similar to that measured for wild-type α T . However, unlike the wild-type protein, the GDP-bound form of α T E203A was constitutively active toward the effector of transducin, the cyclic guanosine monophosphate phosphodiesterase. Thus, the α T E203A mutant represents a short-circuited protein switch that no longer requires GTP for the activation of the effector target phosphodiesterase.