Improved purification of transducin subunits from bovine retinal rod outer segments

Transducin serves as a mediator between the receptor protein, rhodopsin, and the effector protein, cGMP phosphodiesterase, in the visual process. Transducin is a protein composed of three polypeptides: T alpha, T beta, and T gamma, and acts as two functional units, the alpha-subunit and the beta gamma-complex. In the present study, I describe an efficient and fast method of purifying T alpha and T beta gamma using chromatography on a blue agarose column connected in tandem with an omega-amino octylagarose column. The recombination of T alpha and T beta gamma reconstitutes the functional heterotrimeric holoprotein, as demonstrated by the recovery of three native properties of transducin: 1) its capacity to exchange guanine nucleotide, 2) its GTP hydrolytic activity, and 3) the ADP-ribosylation of T alpha catalysed by pertussis toxin.