Transducin activation by rhodopsin without a covalent bond to the 11-cis-retinal chromophore.
Rhodopsin and the visual pigments are a distinct group within the family of G-protein-linked receptors in that they have a covalently bound ligand, the 11-cis-retinal chromophore, whereas all of the other receptors bind their agonists through noncovalent interactions. The retinal chromophore in rhodopsin is bound by means of a protonated Schiff base linkage to the epsilon-amino group of Lys-296. Two rhodopsin mutants have been constructed, K296G and K296A, in which the covalent linkage to the chromophore is removed. Both mutants form a pigment with an absorption spectrum close to that of the wild type when reconstituted with the Schiff base of an n-alkylamine and 11-cis-retinal. In addition, the pigment formed from K296G and the n-propylamine Schiff base of 11-cis-retinal was found to activate transducin in a light-dependent manner, with 30 to 40% of the specific activity measured for the wild-type protein. It appears that the covalent bond is not essential for binding of the chromophore or for catalytic activation of transducin.
Zhukovsky
E A
EA
Graduate Department of Biochemistry, Brandeis University, Waltham, MA 02254.
Robinson
P R
PR
Oprian
D D
DD
D001665:Binding Sites; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D012172:Retinaldehyde / Q000378:metabolism*; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D012545:Schiff Bases; D013053:Spectrophotometry; D015293:Transducin / Q000378:metabolism* / Q000528:radiation effects
D012545:Schiff Bases; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012243:Rhodopsin; D015293:Transducin; D012172:Retinaldehyde