Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
J Am Chem Soc. 2010 Jun 9;132(22):7709-19. doi: 10.1021/ja101691s.
Nuclear quadrupolar couplings are sensitive probes of hydrogen bonding. Experimental quadrupolar coupling constants of alpha deuterons (D(alpha) QCC) are reported for the residues of human ubiquitin that do not experience large-amplitude internal dynamics on the pico- to nanosecond time scale. Two different methods for D(alpha) QCC estimation are employed: (i) direct estimation of D(alpha) QCC values from R(1) and R(2) (2)H D(alpha) rates using the dynamics parameters (S(C(alpha)-H(alpha))(2)) derived from 1 micros molecular dynamics simulations as well as from (13)C(alpha) relaxation measurements and (ii) indirect measurements via scalar relaxation of the second kind that affects (13)C(alpha) relaxation rates in (13)C(alpha)-D(alpha) spin systems. A relatively large variability of D(alpha) QCC values is produced by both methods. The average value of 170.6 +/- 3 kHz is derived from the combined data set, with D(alpha) QCC values ranging from 159.2 to 177.2 kHz. The set of lowest quadrupolar couplings in all data sets corresponds to the residues that are likely to form weak C(alpha)-H(alpha)...O=C hydrogen bonds as predicted from the analysis of short H(alpha)...O distances in three-dimensional structures of ubiquitin. These D(alpha) nuclei show up to 10 kHz reduction in their QCC values, which is in agreement with earlier solid-state NMR measurements in alpha deuterons of glycine. A statistically significant correlation is observed between the QCC values of alpha-deuterons and the inverse cube of C(alpha)-H(alpha)...O=C distances in ubiquitin.
核四极矩耦合是氢键的灵敏探针。报告了人泛素中不经历皮秒至纳秒时间尺度上大幅度内动力学的残基的α氘（D（α）QCC）的实验四极矩耦合常数。采用两种不同的方法估计 D（α）QCC：（i）使用从 1 μs 分子动力学模拟中得出的动态参数（S（C（α）-H（α））（2））以及从 13C（α）弛豫测量值直接从 R（1）和 R（2）（2）H D（α）速率估计 D（α）QCC 值；（ii）通过影响 13C（α）-D（α）自旋系统中的 13C（α）弛豫速率的第二类标量弛豫来间接测量。两种方法都产生了 D（α）QCC 值的较大变化性。从合并数据集得出的平均值为 170.6 ± 3 kHz，D（α）QCC 值范围为 159.2 至 177.2 kHz。所有数据集的最低四极矩耦合的集合对应于那些可能形成弱 C（α）-H（α）...O=C氢键的残基，这是从三维结构中 H（α）...O 距离的分析预测的。这些 D（α）核的 QCC 值最多降低 10 kHz，这与甘氨酸中α氘的早期固态 NMR 测量结果一致。在泛素中，观察到 D（α）氘的 QCC 值与 C（α）-H（α）...O=C 距离的立方倒数之间存在显著的相关性。
