Presence of Two Rhodopsin Intermediates Responsible for Transducin Activation
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- 作者：Shuji Tachibanaki ; Hiroo Imai ; Taku Mizukami ; Tetsuji Okada ; Yasushi Imamoto ; Takahiko Matsuda ; Yoshitaka Fukada ; Akihisa Terakita ; and Yoshinori Shichida
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：November 18, 1997
- 年：1997
- 卷：36
- 期：46
- 页码：14173 - 14180
- 全文大小：189K
- 年卷期：v.36,no.46(November 18, 1997)
- ISSN：1520-4995
文摘
To identify how many rhodopsin intermediates interactwith retinal G-protein transducin, thephotobleaching process of chicken rhodopsin has been investigated inthe presence or absence of transducinby means of time-resolved low-temperature spectroscopy. Singularvalue decomposition (SVD) analysisof the spectral data showed that a new intermediate called metaIb is present between formally identifiedmetarhodopsin I (now referred to as meta Ia) andmetarhodopsin II (meta II). Since the absorptionmaximumof meta Ib (460 nm) is similar to that of metaIa (480 nm), but considerably different from that ofmetaII (380 nm), meta Ib should have a protonated retinylideneSchiff base as its chromophore. Whereastransducin showed no effect on the conversion process betweenlumirhodopsin (lumi) and meta Ia, itaffected the process between meta Ia and metaIb and that between meta Ib and meta II.These resultssuggest that at least two intermediates (meta Ib and metaII) interact with transducin. The addition ofGTP
S had no effect on the meta Ib-transducininteraction, while it abolished the ability of transducinto interact with meta II. Thus, meta Ib only binds totransducin, while meta II catalyzes a GDP-GTPexchange in transducin. These results suggest that deprotonationof the Schiff base chromophore is notnecessary for the binding to transducin, while changes in proteinstructure including Schiff basedeprotonation are needed to induce the GDP-GTP exchange intransducin.
S had no effect on the meta Ib-transducininteraction, while it abolished the ability of transducinto interact with meta II. Thus, meta Ib only binds totransducin, while meta II catalyzes a GDP-GTPexchange in transducin. These results suggest that deprotonationof the Schiff base chromophore is notnecessary for the binding to transducin, while changes in proteinstructure including Schiff basedeprotonation are needed to induce the GDP-GTP exchange intransducin.