MacKenzie K R, Prestegard J H, Engelman D M
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA.
J Biomol NMR. 1996 May;7(3):256-60. doi: 10.1007/BF00202043.
We have used a spin-echo difference NMR pulse sequence to measure three-bond J couplings between lambda- and alpha-carbons of the leucine residues in a micelle-associated helical peptide dimer that corresponds to residues 62-101 of the transmembrane erythrocyte protein glycophorin A. The observed 3J couplings correlate strongly with the 13C chemical shift of the lambda-methyl groups, and within experimental error both the shift distribution of the methyl carbons and the variations in 3J can be accounted for by variations in side-chain rotamer populations. We infer that all leucine side chains in this peptide dimer are in fast exchange among chi 2 rotamers and sample two of the three possible rotameric states, even when the side chain forms part of the dimer interface. The observed correlation of chemical shift with couplings can be traced to a gamma-gauche interaction of methyl and alpha-carbons. This correlation may provide an alternate route to rotamer analysis in some protein systems.
我们使用自旋回波差分核磁共振脉冲序列，来测量与跨膜红细胞蛋白血型糖蛋白A的62 - 101位残基相对应的胶束相关螺旋肽二聚体中亮氨酸残基的λ-碳和α-碳之间的三键J耦合。观察到的3J耦合与λ-甲基的13C化学位移密切相关，并且在实验误差范围内，甲基碳的位移分布和3J的变化都可以通过侧链旋转异构体群体的变化来解释。我们推断，即使侧链构成二聚体界面的一部分，该肽二聚体中的所有亮氨酸侧链也在χ2旋转异构体之间快速交换，并采样三种可能旋转异构体状态中的两种。观察到的化学位移与耦合之间的相关性可追溯到甲基和α-碳之间的γ-gauche相互作用。这种相关性可能为某些蛋白质系统中的旋转异构体分析提供另一种途径。
