Time-resolved x-ray diffraction reveals movement of F helix of D96N bacteriorhodopsin during M-MN transition at neutral pH

被引:20
作者
Oka, T
Yagi, N
Tokunaga, F
Kataoka, M [1 ]
机构
[1] Nara Inst Sci & Technol, Grad Sch Mat Sci, Nara 6300101, Japan
[2] Osaka Univ, Fac Sci, Dept Earth & Space Sci, Osaka 5600043, Japan
[3] RIKEN Harima Inst, Sayo, Hyogo 6795148, Japan
[4] Japan Synchrotron Radiat Res Inst, Life & Environm Div, Sayo, Hyogo 6795198, Japan
关键词
D O I
10.1016/S0006-3495(02)75602-6
中图分类号
Q6 [生物物理学];
学科分类号
071011 ;
摘要
D96N bacteriorhodopsin has two photointermediates with the deprotonated Schiff base: the M and MN intermediates. We measure the time-resolved x-ray diffraction of the D96N purple membrane after flash photoexcitation (pH 7.0, 25 degreesC). The data clearly show the M-MN transition during the D96N photocycle. Low-resolution projection maps of these states show that the F helix of the MN intermediate shifts from its original position and this shift is much larger than that of the M intermediate. This indicates that the F helix moves in the M-MN transition of the D96N bacteriorhodopsin photocycle. Moreover, the existence of the MN intermediate in the D96N photocycle under neutral pH indicates that the MN intermediate is not peculiar to the alkaline condition. It is notable that the structural transition of M-MN is independent of the protonation state of the Schiff base. Therefore, the F helix movement precedes reprotonation of the Schiff base in the bacteriorhodopsin photocycle. Our previous study showed that the M-MN transition is hydration-dependent and that the MN intermediate is more hydrated than the M intermediate. Considering this together with the present results, we conclude that the movement of the F helix causes hydration of the cytoplasmic side, which promotes the reprotonation of the Schiff base.
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收藏
页码:2610 / 2616
页数:7
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