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首页> 外文期刊>Journal of Molecular Biology >Side-chains in native and random coil protein conformations. Analysis of NMR coupling constants and chi(1) torsion angle preferences
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Side-chains in native and random coil protein conformations. Analysis of NMR coupling constants and chi(1) torsion angle preferences

机译：天然和随机卷曲蛋白构象中的侧链。 NMR耦合常数和chi（1）扭转角首选项的分析

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The behaviour of amino acid side-chains in proteins in solution has been characterised by analysing NMR (3)J(H alpha H beta) coupling constants and crystallographic chi(1) torsion angles. Side-chains both in the core of native folded proteins and in situations where there is an absence of close packing including the random coil state have been considered. An analysis of experimental (3)J(H alpha H beta) coupling constant data for ten proteins shows that in the core of native proteins a very close similarity is observed between the chi(1) conformations adopted in solution and in crystals. There is clear evidence, however, for significant motional averaging about the chi(1) torsion angles in solution. Using a model of a Gaussian distribution about the average torsion angles the extent of these fluctuations has been quantified; the standard deviation for the motion is 26 degrees, the fluctuations about chi(1) in the protein core being similar in size to those found for main-chain phi torsion angles in solution. From the distribution of chi(1) torsion angles in a data base of protein crystal structures, torsion angle populations and coupling constants have been predicted for a random coil polypeptide. Significant variations in the chi(1) distributions for different amino acids give differences in the predicted coupling constants; for (3)J(H alpha H beta), for example, values of 5.1 and 5.7 Hz are predicted for serine compared with 4.9 and 9.9 Hz for leucine. Experimental data for short unstructured peptides show an excellent agreement with the predictions, indicating that the overall chi(1) distributions in protein crystals reflect the local preferences of the amino acids. Predictions from the protein data base therefore provide an important framework for interpreting experimental data for nonnative protein conformations and for residues on the surface of folded proteins. (C) 1998 Academic Press. [References: 54]
机译：溶液中蛋白质中氨基酸侧链的行为已通过分析NMR（3）J（H alpha H beta）耦合常数和晶体学chi（1）扭转角进行了表征。已经考虑了天然折叠蛋白核心中的侧链以及在没有紧密堆积（包括随机卷曲状态）的情况下的侧链。对十种蛋白质的实验性（3）J（HαHβ）偶联常数数据的分析表明，在天然蛋白质的核心中，溶液和晶体中采用的chi（1）构象之间观察到非常相似的相似性。但是，有明显的证据表明，在解决方案中，chi（1）扭转角的运动平均值很高。使用关于平均扭转角的高斯分布模型，已对这些波动的程度进行了量化。运动的标准偏差为26度，蛋白质核心中chi（1）的波动大小与溶液中主链phi扭转角的波动大小相似。根据chi（1）扭转角在蛋白质晶体结构数据库中的分布，已经预测了随机线圈多肽的扭转角种群和耦合常数。不同氨基酸的chi（1）分布的显着变化会导致预测的偶联常数有所不同;例如，对于（3）J（H alpha H beta），丝氨酸的预测值为5.1和5.7 Hz，而亮氨酸的预测值为4.9和9.9 Hz。短的非结构化肽的实验数据显示出与预测的极好的一致性，表明蛋白质晶体中的整体chi（1）分布反映了氨基酸的局部偏好。因此，蛋白质数据库的预测为解释非天然蛋白质构象和折叠蛋白质表面上的残基的实验数据提供了重要的框架。 （C）1998年学术出版社。 [参考：54]

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