title: A structural model for the alpha-subunit of transducin. Implications of its role as a molecular switch in the visual signal transduction mechanism.
abstract: Transducin is a GTP-binding protein which mediates the light activation signal from photolyzed rhodopsin to cGMP phosphodiesterase and is pivotal in the visual excitation process. Biochemical studies suggest that the T alpha subunit of transducin is composed of three functional domains, one for rhodopsin/T beta gamma interaction, another for guanine nucleotide binding, and a third for the activation of phosphodiesterase. The integration of the primary sequence of T alpha along with secondary structure, hydropathy and folding topology predictions, and a comparison with homologous proteins have led to the construction of a three-dimensional model of the T alpha subunit. A molecular mechanism which underlies the coupling action of T alpha is suggested on the basis of this model.
mesh_terms: D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism; D008027:Light; D008565:Membrane Proteins / Q000502:physiology*; D008956:Models, Chemical; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010786:Photoreceptor Cells / Q000378:metabolism; D011487:Protein Conformation; D012243:Rhodopsin / Q000378:metabolism; D013329:Structure-Activity Relationship; D015293:Transducin; D014796:Visual Perception / Q000502:physiology*
chemical_list: D008565:Membrane Proteins; D012243:Rhodopsin; D010727:Phosphoric Diester Hydrolases; D019204:GTP-Binding Proteins; D015293:Transducin