Relative orientation between the beta-ionone ring and the polyene chain for the chromophore of rhodopsin in native membranes.
Relative orientation between the beta-ionone ring and the polyene chain for the chromophore of rhodopsin in native membranes.
复制标题
天然膜中视紫红质发色团的 β-紫罗兰酮环和多烯链之间的相对方向。
作者：
P. Spooner;J. Sharples;M. Verhoeven;J. Lugtenburg;C. Glaubitz;A. Watts
本文用旋转共振固体核磁共振方法测定了牛视网膜视紫红质发色团11-Z-亚视黄基的β-紫罗酮环和多烯链的相对取向。用11-Z-[8，18-（13）C（2）]视黄醛或11-Z-[8，16/17（13）C（2）]视黄醛再生漂白的蛋白质，后者在化学等价的位置16和17中的任一个上仅具有一个（13）C标记。观察到（13）C选择性地富集在环甲基，C16/17，揭示了环的替代构象状态。次要光谱组分占发色团的约26%。主要构象（约74%）具有测量核间距离所需的化学位移分辨率（13）C在视网膜链（C8）分别从这些甲基。得到的距离约束，C8到C16和C17（4.05 +/- 0.25 A）和从C8到C18（2.95 +/- 0.15 A），表明视紫红质中的亚视黄基的主要部分具有扭曲的6-s-顺式构象。这里在C8和C18之间进行的更精确的距离测量（2.95 A）预测链相对于环以适度的量扭曲到平面外（C5-C6-C7-C8扭转角= -28 +/-7度）。
Rotational resonance solid state nuclear magnetic resonance has been used to determine the relative orientation of the beta-ionone ring and the polyene chain of the chromophore 11-Z-retinylidene of rhodopsin in rod outer segment membranes from bovine retina. The bleached protein was regenerated with either 11-Z-[8,18-(13)C(2)]retinal or 11-Z-[8,16/17(13)C(2)]retinal, the latter having only one (13)C label at either of the chemically equivalent positions 16 and 17. Observation of (13)C selectively enriched in the ring methyl groups, C16/17, revealed alternative conformational states for the ring. Minor spectral components comprised around 26% of the chromophore. The major conformation (approximately 74%) has the chemical shift resolution required for measuring internuclear distances to (13)C in the retinal chain (C8) separately from each of these methyl groups. The resulting distance constraints, C8 to C16 and C17 (4.05 +/- 0.25 A) and from C8 to C18 (2.95 +/- 0.15 A), show that the major portion of retinylidene in rhodopsin has a twisted 6-s-cis conformation. The more precise distance measurement made here between C8 and C18 (2.95 A) predicts that the chain is twisted out-of-plane with respect to the ring by a modest amount (C5-C6-C7-C8 torsion angle = -28 +/- 7 degrees ).