Nuclear Magnetic Resonance--new Methods And Molecular St

我们继续我们对生物大分子的研究，这些大分子相对于磁场是弱排列的。~(31)P化学位移各向异性和~(31)P-H_3？偶极偶联独立地验证了从偶极偶合得到的模型DNA寡核苷酸的结构比传统的核磁共振结构或在结晶态观察到的结构要准确得多。示踪扩散各向异性测量表明，常用的双孔液晶介质不是由圆盘组成，而是由强烈穿孔的双层组成。对最近提出的用于排列大分子的凝胶法进行了改进，允许凝胶拉伸而不是压缩。这是第一次证明了洗涤剂增溶的多肽可以在这样的介质中排列，为研究这种系统提供了新的机会。钙-钙调蛋白的偶极耦合研究表明，N-末端结构域的螺旋间角与结晶态的螺旋间角有很大的不同，表明这种调节蛋白具有相当大的可塑性。相反，大多数与靶相互作用的残基的侧链chi-1角被锁定在单一的旋转体状态，而靶相互作用表面的局部可塑性由8个蛋氨酸残基的chi-2和chi-3角的柔性控制。

We have continued our study of biological macromolecules that are weakly aligned relative to the magnetic field. Study of 31P chemical shift anisotropy and 31P-H3? dipolar couplings independently validate that the structure derived of a model DNA oligonucleotide derived from dipolar couplings is considerably more accurate than the conventional NMR structure or structures observed in the crystalline state. Tracer diffusion anisotropy measurements indicate that the commonly used bicellar liquid crystalline medium does not consist of disks but of strongly perforated bilayers. A modification to the recently proposed gel method for aligning macromolecules has been developed that permits stretching of the gel instead of compression. It has been demonstrated for the first time that detergent-solubilized polypeptides can be aligned in such a medium, providing new opportunities for the study of such systems. A dipolar coupling study of Ca2+-calmodulin reveals that the interhelical angles in the N-terminal domain differ substantially from those observed in the crystalline state, indicative of considerable plasticity in this regulatory protein. In contrast, the sidechain chi-1 angles of the majority of target-interacting residues are locked into a single rotameric state, and local plasticity in the target-interacting surface is dominated by flexibility in the chi-2 and chi-3 angles of 8 methionine residues.