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  • Title: Effects of carboxyl methylation of photoreceptor G protein gamma-subunit in visual transduction.
    Author: Fukada Y, Matsuda T, Kokame K, Takao T, Shimonishi Y, Akino T, Yoshizawa T.
    Journal: J Biol Chem; 1994 Feb 18; 269(7):5163-70. PubMed ID: 8106497.
    Abstract:
    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.
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