Effects of carboxyl methylation of photoreceptor G protein gamma-subunit in visual transduction.
G protein gamma-subunits are isoprenylated and carboxyl-methylated at the C-terminal cysteine, which is indispensable for the function of photoreceptor G protein transducin (T alpha beta gamma). However, the physiological role of the methylation and its reversibility have been unclear. Here we isolated methylated and non-methylated forms of farnesylated T beta gamma, and demonstrated that the methylation remarkably facilitates not only the membrane association of T beta gamma but also the subunit interaction between T alpha and T beta gamma. Consequently, the functional coupling of transducin with light-activated receptor, metarhodopsin II, was stabilized by the methylation, resulting in acceleration of GTP gamma S (guanosine 5'-3-O-(thio) triphosphate) binding to T alpha. An examination of the reversibility of the methylation suggested that T gamma is kept fully methylated in rod outer segments. These observations indicate that the methylation of T gamma plays an important role in the most efficient photon-signal transduction process in rod cells.
Fukada
Y
Y
Department of Pure and Applied Sciences, College of Arts and Sciences, University of Tokyo, Japan.
Matsuda
T
T
Kokame
K
K
Takao
T
T
Shimonishi
Y
Y
Akino
T
T
Yoshizawa
T
T
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D003624:Darkness; D005204:Farnesol / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008027:Light; D046911:Macromolecular Substances; D008745:Methylation; D008861:Microsomes / Q000378:metabolism*; D017368:Protein Prenylation; D011499:Protein Processing, Post-Translational; D011892:Rana catesbeiana; D012243:Rhodopsin / Q000031:analogs & derivatives* / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D015293:Transducin / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014785:Vision, Ocular / Q000502:physiology*
D046911:Macromolecular Substances; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D005204:Farnesol; C013110:metarhodopsins; D012243:Rhodopsin; D015293:Transducin