Gibson S K, Parkes J H, Liebman P A
Department of Biochemistry and Biophysics, University of Pennsylvania Medical Center, Philadelphia 19104-6059, USA.
Biochemistry. 1998 Aug 18;37(33):11393-8. doi: 10.1021/bi980933w.
Deactivation of many G protein coupled receptors (GPCRs) is now known to require phosphorylation of the activated receptor. The first such GPCR so analyzed was rhodopsin, which upon light activation forms an intramolecular equilibrium between the two conformers, metarhodopsin I and II (MI and MII). In this study, we find surprisingly that rhodopsin phosphorylation increases rather than diminishes the formation of MII, the conformation that activates G protein. The MI-MII equilibrium constant was progressively shifted toward MII as the experimental phosphorylation stoichiometry was increased from 0 to 6.4 phosphates per rhodopsin. Increasing phosphorylation both increased MII's formation rate (k1) and decreased its rate of loss (k-1). The direct effect of cytoplasmic surface phosphorylation on intramolecular conformer equilibria observed here may be important to functional state modulation of other membrane proteins.
现在已知许多G蛋白偶联受体（GPCR）的失活需要对激活的受体进行磷酸化。第一个经过此类分析的GPCR是视紫红质，它在光激活后会在两种构象体（视紫红质I和II，即MI和MII）之间形成分子内平衡。在本研究中，我们惊讶地发现视紫红质磷酸化增加而非减少了激活G蛋白的构象体MII的形成。随着实验性磷酸化化学计量从每个视紫红质0个磷酸盐增加到6.4个磷酸盐，MI-MII平衡常数逐渐向MII偏移。磷酸化增加既提高了MII的形成速率（k1），又降低了其消失速率（k-1）。此处观察到的细胞质表面磷酸化对分子内构象体平衡的直接影响可能对其他膜蛋白的功能状态调节很重要。
