A comprehensive analysis of multifield 15N relaxation parameters in proteins:: Determination of 15N chemical shift anisotropies
A comprehensive analysis of multifield 15N relaxation parameters in proteins:: Determination of 15N chemical shift anisotropies
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DOI：
10.1021/ja0038676
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发表时间：
2001-05-16
影响因子：
15
通讯作者：
Roumestand, C
中科院分区：
文献类型：
--
作者：
Canet, D;Barthe, P;Roumestand, C
本研究涉及利用三个经典的N-15弛豫参数（纵向弛豫率，R-1，横向弛豫率，R-2，和H-1-N-15交叉弛豫率，σ（NH））在几个磁场中测量均匀的N-15标记的蛋白质。根据函数形式A + B/（1 + omega（2）tau（2）（x））分析R-1、R-2和sigma（NH）中涉及的谱密度，其中tau（s）是与NH矢量在其所属的残差水平上感测到的慢运动相关联的相关时间。系数B提供了主干动力学的真实视图，而A与快速局部运动相关联。根据“无模型方法”，B可以用2 τ S-s（2）来识别，其中S是广义序参量。相关时间τ（s）由弛豫参数的场依赖性确定，而A和B通过线性方程确定。需要这种简单的数据处理来获得基于统计方法的真实误差条。这被证明是验证扩展分析的关键点，旨在确定氮化学位移各向异性。蛋白质C12 A-p8（MTCP 1）已被选为本研究的模型。它将表明，所有的数据（在对应于质子共振的400，500，600，700，和800 MHz的五个磁场强度获得）是非常一致的拟合，提供了一个特定的有效相关时间与慢动作被定义为每个残基。这是通过实验值和重新计算值之间的微小偏差来评估的，在所有情况下，这些偏差都保持在实验不确定性范围内。这种策略使得不必要的复杂方法基于几个慢动作或其可能的各向异性的组合。在蛋白质的核心内，tau（s）在相对窄的范围内波动（平均值为6.15 ns，均方根偏差为0.36 ns），而在蛋白质末端处则显著降低（下降至接近3 ns）。在一定程度上，这些波动与蛋白质结构相关。A的获得没有足够的精确度来进行有价值的讨论。相反，从B导出的顺序参数表现出与蛋白质结构的显着相关性。最后，多场分析的纵向和横向弛豫速率的演变已被细化，允许N-15化学位移各向异性（CSA），以不同的残留物。在不确定性（在统计的基础上得出），几乎恒定的值。这强烈表明，对于蛋白质中给定的残基获得的该参数的实验值、该残基的性质以及该残基可能参与蛋白质的结构化区域之间不存在相关性。
This study deals with the exploitation of the three classical N-15 relaxation parameters (the longitudinal relaxation rate, R-1, the transverse relaxation rate, R-2, and the H-1-N-15 cross-relaxation rate, sigma (NH)) measured at several magnetic fields in uniformly N-15-labeled proteins. Spectral densities involved in R-1, R-2 and sigma (NH) are analyzed according to the functional form A + B/(1 + omega (2)tau (2)(x)), where tau (s) is the correlation time associated with slow motions sensed by the NH vector at the level of the residue to which it belongs. The coefficient B provides a realistic view of the backbone dynamics, whereas A is associated with fast local motions. According to the "model free approach", B can be identified with 2 tau S-s(2) where S is the generalized order parameter. The correlation time tau (s) is determined from the field dependency of the relaxation parameters while A and B are determined through linear equations. This simple data processing is needed for obtaining realistic error bars based on a statistical approach. This proved to be the key point for validating an extended analysis aiming at the determination of nitrogen chemical shift anisotropy. The protein C12A-p8(MTCP1) has been chosen as a model for this study. It will be shown that all data (obtained at five magnetic field strengths corresponding to proton resonance of 400, 500, 600, 700, and 800 MHz) are very consistently fitted provided that a specific effective correlation time associated with slow motions is defined for each residue. This is assessed by small deviations between experimental and recalculated values, which, in all cases, remain within experimental uncertainty. This strategy makes needless elaborate approaches based on the combination of several slow motions or their possible anisotropy. Within the core of the protein tau (s) fluctuates in a relatively narrow range (with a mean value of 6.15 ns and a root-mean-square deviation of 0.36 ns) while it is considerably reduced at the protein extremities (down to similar to3 ns). To a certain extent, these fluctuations are correlated with the protein structure. A is not obtained with sufficient accuracy to be valuably discussed. Conversely, order parameters derived from B exhibit a significant correlation with the protein structure. Finally, the multi-field analysis of the evolution of longitudinal and transverse relaxation rates has been refined by allowing the N-15 chemical shift anisotropy (csa) to vary residue by residue. Within uncertainties (derived here on a statistical basis) an almost constant value is obtained. This strongly indicates an absence of correlation between the experimental value of this parameter obtained for a given residue in the protein, the nature of this residue, and the possible involvement of this residue in a structured area of the protein.