FTIR Studies of the Photoactivation Processes in Squid Retinochrome
详细信息 查看全文
- 作者：Yuji Furutani ; Akihisa Terakita ; Yoshinori Shichida ; and Hideki Kandori
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：June 7, 2005
- 年：2005
- 卷：44
- 期：22
- 页码：7988 - 7997
- 全文大小：225K
- 年卷期：v.44,no.22(June 7, 2005)
- ISSN：1520-4995
文摘
Retinochrome is a photoisomerase of the invertebrate visual system, which converts all-trans-retinal to the 11-cis configuration and supplies it to visual rhodopsin. In this paper, we studied light-induced structural changes in squid retinochrome by means of low-temperature UV-visible and Fouriertransform infrared (FTIR) spectroscopy. In PC liposomes, lumi-retinochrome was stable in the widetemperature range between 77 and 230 K. High thermal stability of the primary intermediate in retinochromeis in contrast to the case in rhodopsins. FTIR spectroscopy suggested that the chromophore of lumi-retinochrome is in a relaxed planar 11-cis form, being consistent with its high thermal stability. Thechromophore binding pocket of retinochrome appears to accommodate both all-trans and 11-cis formswithout a large distortion, and limited protein structural changes between all-trans and 11-cis chromophoresmay be suitable for the function of retinochrome as a photoisomerase. The analysis of N-D and O-Dstretching vibrations in D2O revealed that the hydrogen bond of the Schiff base is weaker in retinochromethan in bovine rhodopsin and bacteriorhodopsin, while retinochrome has a water molecule under stronglyhydrogen-bonded conditions (O-D stretch at 2334 cm-1). The hydrogen bond of the water is furtherstrengthened in lumi-retinochrome. The formation of meta-retinochrome accompanies deprotonation ofthe Schiff base, together with the peptide backbone alterations of 
-helices, and possible formation of
-sheets. It was found that the Schiff base proton is not transferred to its counterion, Glu181, but directlyreleased to the aqueous phase in PC liposomes (pH 7.5). This suggests that the Schiff base environmentis exposed to solvent in meta-retinochrome, which may be advantageous for the hydrolysis reaction ofthe Schiff base in the transport of 11-cis-retinal to its shuttle protein.
-helices, and possible formation of-sheets. It was found that the Schiff base proton is not transferred to its counterion, Glu181, but directlyreleased to the aqueous phase in PC liposomes (pH 7.5). This suggests that the Schiff base environmentis exposed to solvent in meta-retinochrome, which may be advantageous for the hydrolysis reaction ofthe Schiff base in the transport of 11-cis-retinal to its shuttle protein.