Light-dependent activation of rod transducin by pineal opsin.
The pineal gland expresses a unique member of the opsin family (P-opsin; Max, M., McKinnon, P. J., Seidenman, K. J., Barrett, R. K., Applebury, M. L., Takahashi, J. S., and Margolskee, R. F. (1995) Science 267, 1502-1506) that may play a role in circadian entrainment and photo-regulation of melatonin synthesis. To study the function of this protein, an epitope-tagged P-opsin was stably expressed in an embryonic chicken pineal cell line. When incubated with 11-cis-retinal, a light-sensitive pigment was formed with a lambdamax at 462 +/- 2 nm. P-opsin bleached slowly in the dark (t1/2 = 2 h) in the presence of 50 mM hydroxylamine. Purified P-opsin in dodecyl maltoside activated rod transducin in a light-dependent manner, catalyzing the exchange of more than 300 mol of GTPgammaS (guanosine 5'-O-(3-thiotriphosphate))/mol of P-opsin. The initial rate for activation (75 mol of GTPgammaS bound/mol of P-opsin/min at 7 microM) increased with increasing concentrations of transducin. The addition of egg phosphatidylcholine to P-opsin had little effect on the activation kinetics; however, the intrinsic rate of decay in the absence of transducin was accelerated. These results demonstrate that P-opsin is an efficient catalyst for activation of rod transducin and suggest that the pineal gland may contain a rodlike phototransduction cascade.
Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, New York 10029, USA. max@msvax.mssm.edu
M
M
Max
A
A
Surya
J S
JS
Takahashi
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RF
Margolskee
B E
BE
Knox
D000818:Animals; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000378:metabolism; D002642:Chick Embryo; D010860:Pigments, Biological; D010870:Pineal Gland / Q000378:metabolism*; D011485:Protein Binding; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism / Q000528:radiation effects*; D012172:Retinaldehyde / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism*; D015293:Transducin / Q000378:metabolism*
D010860:Pigments, Biological; D017299:Rod Opsins; D015293:Transducin; D012172:Retinaldehyde