Farnesylated gamma-subunit of photoreceptor G protein indispensable for GTP-binding.
Transducin, composed of subunits T alpha, T beta and T gamma, is a member of a heterotrimeric G-protein family, and transduces the light signal in visual cells. We have recently found that bovine T beta gamma can be separated into two components. T beta gamma-1 and T beta gamma-2, each of which has its own gamma-subunit, T gamma-1 and T gamma-2, respectively. T beta gamma-2 enhances the binding of GTP to T alpha in the presence of metarhodopsin II by about 30-fold compared with T beta gamma-1. Here we show that a farnesyl moiety is attached to a sulphur atom of the C-terminal cysteine of T gamma-2 (active form), a part of which is additionally methyl-esterified at the alpha-carboxyl group. In T gamma-1 (inactive form), however, such modifications are missing. Thus, the farnesyl moiety attached to the gamma-subunit is indispensable for the GTP-binding activity of transducin. This suggests that a similar modification may occur in the gamma-subunits of other heterotrimeric G proteins involved in biological signal transduction processes.
Fukada
Y
Y
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Takao
T
T
Ohguro
H
H
Yoshizawa
T
T
Akino
T
T
Shimonishi
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine; D005204:Farnesol; D006160:Guanosine Triphosphate / Q000378:metabolism*; D046911:Macromolecular Substances; D013058:Mass Spectrometry; D008745:Methylation; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000302:isolation & purification; D010786:Photoreceptor Cells / Q000032:analysis*; D012697:Serine Endopeptidases; D015398:Signal Transduction; D015293:Transducin / Q000378:metabolism*
D046911:Macromolecular Substances; D010446:Peptide Fragments; D005204:Farnesol; D006160:Guanosine Triphosphate; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; D015293:Transducin; D003545:Cysteine