A three-dimensional difference map of the N intermediate in the bacteriorhodopsin photocycle: part of the F helix tilts in the M to N transition.
A three-dimensional difference map of the N intermediate in the bacteriorhodopsin photocycle: part of the F helix tilts in the M to N transition.
复制标题
细菌视紫红质光循环中 N 中间体的三维差异图：F 螺旋的一部分在 M 到 N 的过渡中倾斜。
DOI：
10.1021/bi952663c
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Vonck,J
中科院分区：
文献类型：
--
作者：
Vonck,J
细菌视紫红质光循环的N中间体被捕获在定点突变体Phe219→leu的葡萄糖包埋样品中进行电子衍射研究。在中性pH条件下，该突变体的N-BR差值傅里叶变换红外光谱与已报道的野生型细菌视紫红质在碱性pH条件下的差值光谱难以区分。投影中N中间体的电子衍射差图在F和G螺旋附近显示出很大的差异，这与Asp96→Gly突变体的M中间体中的特征非常相似[Subramaniam等人。(1993年)EMBO J.12，1−8]。这种相似性是根据傅里叶变换红外数据预测的，这些数据表明，Asp96突变体中的M中间体已经具有N中间体的蛋白质结构[Sasaki等人。(1992年)生物化学267,20782−20786]。由倾斜25°的样品的电子衍射数据计算出的N中间体的初步三维差图清楚地表明，F螺旋上的变化包括螺旋的细胞质末端向外移动。此外，G螺旋的细胞质一侧移动或变得更加有序。与已发表的M中间体差值图的比较表明，F螺旋倾斜发生在M到N的转变中，而G螺旋的变化代表了光循环的早期步骤。
The N intermediate of the bacteriorhodopsin photocycle was trapped for electron diffraction studies in glucose-embedded specimens of the site-directed mutant Phe219→Leu. At neutral pH, the N-bR difference Fourier transform infrared spectrum of this mutant is indistinguishable from published difference spectra obtained for wild-type bacteriorhodopsin at alkaline pH. An electron diffraction difference map of the N intermediate in projection shows large differences near the F and the G helix, which are very similar to the features seen in the M intermediates of the Asp96→Gly mutant [Subramaniam et al. (1993)EMBO J.12, 1−8]. This similarity was anticipated on the basis of Fourier transform infrared data, which have shown that the M intermediate trapped in Asp96 mutants already has the protein structure of the N intermediate [Sasaki et al. (1992)J.Biol.Chem.267, 20782−20786]. A preliminary three-dimensional difference map of the N intermediate, calculated from electron diffraction data of samples tilted at 25°, clearly shows that the change on the F helix consists of an outward movement of the cytoplasmic end of the helix. In addition, the cytoplasmic side of the G helix moves or becomes more ordered. Comparison with published difference maps of the M intermediate indicates that the F helix tilt occurs in the M to N transition, but the G helix change represents an earlier step in the photocycle.