Altenbach C, Cai K, Klein-Seetharaman J, Khorana H G, Hubbell W L
Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-7008, USA.
Biochemistry. 2001 Dec 25;40(51):15483-92. doi: 10.1021/bi011546g.
Spin-labeled double mutants of rhodopsin were produced containing a reference nitroxide at position 65, at the cytoplasmic termination of helix TM1, and a second nitroxide in the sequence of residues 306-319, which includes the cytoplasmic termination of helix TM7 and nearly the entire surface helix H8. Magnetic dipole-dipole interactions between the spins are analyzed to provide interspin distance distributions in both the dark and photoactivated states of rhodopsin. The distributions, apparently resulting from the conformational flexibility of the side chains, are found to be consistent with the structural model of rhodopsin in the dark state derived from crystallography. Photoactivation of the receptor triggers an increase in distance between residues in TM7, but not those in H8, relative to the reference at position 65 in TM1. The simplest interpretation of the result is a movement of the cytoplasmic portion of TM7 away from TM1 by 2-4 A.
视紫红质的自旋标记双突变体被制备出来，在螺旋TM1的胞质末端第65位含有一个参比氮氧自由基，在残基序列306 - 319中含有第二个氮氧自由基，该序列包括螺旋TM7的胞质末端以及几乎整个表面螺旋H8。分析自旋之间的磁偶极 - 偶极相互作用，以提供视紫红质在黑暗和光激活状态下的自旋间距离分布。这些分布显然是由侧链的构象灵活性导致的，发现它们与通过晶体学得出的黑暗状态下视紫红质的结构模型一致。相对于TM1中第65位的参比自由基，受体的光激活引发了TM7中残基之间距离的增加，但H8中残基之间的距离没有增加。该结果最简单的解释是TM7的胞质部分远离TM1移动了2 - 4埃。
