Llinás M, Klein M P, Wüthrich K
Biophys J. 1978 Dec;24(3):849-62. doi: 10.1016/S0006-3495(78)85424-1.
The proton nuclear magnetic resonance (NMR) spin-lattice relaxation of all six amides of deferriferrichrome and of various alumichromes dissolved in hexadeutero-dimethylsulfoxide have been investigated at 100, 220, and 360 MHz. We find that, depending on the type of residue (glycyl or ornithyl), the amide proton relaxation rates are rather uniform in the metal-free cyclohexapeptide. In contrast, the (1)H spinlattice relaxation times (T(1)'s) are distinct in the Al(3+)-coordination derivative. Similar patterns are observed in a number of isomorphic alumichrome homologues that differ in single-site residue substitutions, indicating that the spin-lattice relaxation rate is mainly determined by dipole-dipole interactions within a rigid molecular framework rather than by the specific primary structures. Analysis of the data in terms of (1)H-(1)H distances (r) calculated from X-ray coordinates yields a satisfactory linear fit between T(1) (-1) and Sigmar(-6) at the three magnetic fields. Considering the very sensitive r-dependence of T(1), the agreement gives confidence, at a quantitative level, both on the fitness of the crystallographic model to represent the alumichromes' solution conformation and on the validity of assuming isotropic rotational motion for the globular metallopeptides. An extra contribution to the amide proton T(1) (-1) is proposed to mainly originate from the (1)H-(14)N dipolar interaction: this was supported by comparison with measurements on an (15)N-enriched peptide. The nitrogen dipolar contribution to the peptide proton relaxation is discussed in the context of {(1)H}-(1)H nuclear Overhauser enhancement (NOE) studies because, especially at high fields, it can be dominant in determining the amide proton relaxation rates and hence result in a decreased effectiveness for the (1)H-(1)H dipolar mechanism to cause NOE's. From the slope and intersect values of T(1) (-1) vs. Sigmar(-6) linear plots, a number of independent estimates of tau(r), the rotational correlation time, were derived. These and the field-dependence of the T(1)'s yield a best estimate <tau(r)> approximately 0.37 ns, in good agreement with 0.38 ns [unk] <tau(r)> [unk] 0.41 ns, previously determined from (13)C and (15)N spin-lattice relaxation data.
已在100兆赫、220兆赫和360兆赫下研究了去铁铁载体的所有六种酰胺以及溶解于十六氘代二甲基亚砜中的各种铝载体的质子核磁共振（NMR）自旋晶格弛豫。我们发现，根据残基类型（甘氨酰基或鸟氨酰基），无金属环六肽中的酰胺质子弛豫率相当均匀。相比之下，在Al(3+)配位衍生物中，（1）H自旋晶格弛豫时间（T(1)）是不同的。在一些在单一位点残基取代上不同的同构铝载体同系物中观察到了类似的模式，这表明自旋晶格弛豫率主要由刚性分子框架内的偶极 - 偶极相互作用决定，而不是由特定的一级结构决定。根据由X射线坐标计算出的（1）H - （1）H距离（r）对数据进行分析，在三个磁场下，T(1)（-1）与Sigmar(-6)之间得到了令人满意的线性拟合。考虑到T(1)对r的非常敏感的依赖性，这种一致性在定量水平上既让人相信晶体学模型适合代表铝载体溶液构象，也让人相信假设球状金属肽具有各向同性旋转运动的有效性。有人提出酰胺质子T(1)（-1）的额外贡献主要源于（1）H - （14）N偶极相互作用：这通过与对一种（15）N富集肽的测量结果进行比较得到了支持。在{（1）H}-（1）H核Overhauser增强（NOE）研究的背景下讨论了氮偶极对肽质子弛豫的贡献，因为特别是在高场下，它在决定酰胺质子弛豫率方面可能占主导地位，从而导致（1）H - （1）H偶极机制产生NOE的有效性降低。从T(1)（-1）与Sigmar(-6)线性图的斜率和截距值中，得出了旋转相关时间tau(r)的一些独立估计值。这些以及T(1)的场依赖性得出最佳估计值<tau(r)>约为0.37纳秒，与先前从（13）C和（15）N自旋晶格弛豫数据确定的0.38纳秒[unk]<tau(r)>[unk]0.41纳秒非常吻合。
