Sherry A D, Keepers J, James T L, Teherani J
Biochemistry. 1984 Jul 3;23(14):3181-5. doi: 10.1021/bi00309a011.
The carbon- 13 spin-lattice relaxation times and nuclear Overhauser enhancements of the N epsilon-monomethyllysine, N epsilon,N epsilon-dimethyllysine, and N alpha,N alpha-dimethylalanine resonances of 13C-methylated concanavalin A have been measured at three carbon frequencies and compared to the relaxation parameters predicted by several motional models. The experimental parameters cannot be reproduced by a simple dipolar relaxation model which includes isotropic reorientation of the protein plus free internal rotational diffusion of the methyl groups but are well predicted by a wobble in a cone model which includes isotropic reorientation of the protein at 33 ns, free internal rotational diffusion of the methyl groups, and a wobble diffusion which reflects the net motion of the amino acid side chains. The analysis indicates that the methylated epsilon-amino side chains exhibit only slightly more motional freedom than does the methylated N-terminal alpha-amino group and suggests some restriction of methyl group rotation in the dimethylamino residues.
已在三个碳频率下测量了13C甲基化伴刀豆球蛋白A的Nε-单甲基赖氨酸、Nε,Nε-二甲基赖氨酸和Nα,Nα-二甲基丙氨酸共振的碳-13自旋晶格弛豫时间和核Overhauser增强，并与几种运动模型预测的弛豫参数进行了比较。实验参数不能由简单的偶极弛豫模型再现，该模型包括蛋白质的各向同性重排加上甲基的自由内部旋转扩散，但由圆锥内摆动模型很好地预测，该模型包括蛋白质在33纳秒时的各向同性重排、甲基的自由内部旋转扩散以及反映氨基酸侧链净运动的摆动扩散。分析表明，甲基化的ε-氨基侧链仅比甲基化的N端α-氨基表现出略多的运动自由度，并表明二甲基氨基残基中甲基旋转存在一些限制。
