title: Uncoupling of GTP binding from target stimulation by a single mutation in the transducin alpha subunit.
abstract: Glutamic acid-203 of the alpha subunit of transducin (alphaT) 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 alpha(T) yielded an alpha subunit (alpha(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 alpha(T). However, unlike the wild-type protein, the GDP-bound form of alpha(T)E203A was constitutively active toward the effector of transducin, the cyclic guanosine monophosphate phosphodiesterase. Thus, the alpha(T)E203A mutant represents a short-circuited protein switch that no longer requires GTP for the activation of the effector target phosphodiesterase.
authors.affiliation: Department of Pharmacology, Cornell University, Ithaca, NY 14853-6401, USA.
authors.forename: R
authors.initials: R
authors.lastname: Mittal
authors.forename: J W
authors.initials: JW
authors.lastname: Erickson
authors.forename: R A
authors.initials: RA
authors.lastname: Cerione
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000409:Alanine / Q000737:chemistry; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D004789:Enzyme Activation; D018698:Glutamic Acid / Q000737:chemistry; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins; D012243:Rhodopsin / Q000378:metabolism; D015293:Transducin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D018698:Glutamic Acid; D006160:Guanosine Triphosphate; D012243:Rhodopsin; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D015293:Transducin; D000409:Alanine