BACKBONE DYNAMICS OF A HIGHLY DISORDERED 131-RESIDUE FRAGMENT OF STAPHYLOCOCCAL NUCLEASE
BACKBONE DYNAMICS OF A HIGHLY DISORDERED 131-RESIDUE FRAGMENT OF STAPHYLOCOCCAL NUCLEASE
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DOI：
10.1006/jmbi.1994.1598
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发表时间：
1994-09-30
影响因子：
5.6
通讯作者：
SHORTLE, D
中科院分区：
文献类型：
--
作者：
ALEXANDRESCU, AT;SHORTLE, D
为了表征葡萄球菌核酸酶变性状态的动力学性质，测量了作为非变性条件下变性状态模型的131个残基片段的主链N-15核的R（1）、R（2）和NOE弛豫参数。松弛数据表明，节段性运动的幅度范围很广，与随机线圈构象不一致。基于对79个残基的分析，获得了分子旋转相关时间τ（m）的最佳值7.8 ns，对于所述79个残基，可以获得R（1）、R（2）和NOE松弛数据。该值大致对应于纳秒时间尺度上最慢的可检测运动，并且具有与大部分分子的全局翻滚一致的幅度。对于大多数残留物，实验数据可以最充分地描述在一个修改的“无模型”的形式主义，其中包括从内部运动的贡献在一个中间（τ（e））和一个快速的时间尺度（τ（i））在缓慢的整体翻滚（τ（m））的上下文中。广义序参数S-2，它给出了运动的幅度在时间尺度上快于tau（m），与序列的疏水性，并建议链的灵活性和疏水性崩溃的序列倾向之间的关系。在蛋白质中的三个α-螺旋的分数群体显示出与S-2值和疏水性比与固有螺旋倾向更强的相关性。这些观察结果表明，二级结构可能会优先稳定在疏水部分的序列。
In order to characterize the dynamic properties of the denatured state of staphylococcal nuclease, R(1), R(2), and NOE relaxation parameters have been measured for the backbone N-15 nuclei of a 131 residue fragment that serves as a model of the denatured state under non-denaturing conditions. The relaxation data indicate a wide range of amplitudes for segmental motion and are inconsistent with a random coil conformation. An optimal value of 7.8 ns was obtained for the molecular rotational correlation time tau(m) based on the analysis of the 79 residues for which R(1), R(2), and NOE relaxation data could be obtained. This value corresponds roughly to the slowest detectable motion on the nanosecond time scale and is of a magnitude consistent with global tumbling of a large portion of the molecule. For the majority of residues, experimental data could be described most adequately in terms of a modified ''model-free'' formalism which includes contributions from internal motions on both an intermediate (tau(e)) and a fast time scale (tau(i)) in the context of slow overall tumbling (tau(m)). The generalized order parameter S-2, which gives the amplitude of motions on time scales faster than tau(m), correlates with sequence hydrophobicity and suggests a relationship between chain flexibility and sequence propensity for hydrophobic collapse. The fractional populations of three alpha-helices in the protein show a stronger correlation with S-2 values and hydrophobicities than with intrinsic helix propensities. These observations suggest that secondary structure may be preferentially stabilized in hydrophobic segments of the sequence.