SPECIFIC CP ASSIGNMENT & SPECTRAL SIMPLIFICATION IN HETERONUCLEAR SPIN SYSTEM

频率选择性异核极化转移 介绍了旋转固体的技术。在此方法中，弱或 应用中等强度的射频(RF)场来建立 哈特曼-哈恩交叉极化明显依赖于 涉及到的原子核的共振偏移量。在这种情况下。 与交叉极化相结合的光谱诱导滤波 (特定CP)可用于光谱简化或 异核自旋对中的赋值目的。频率选择性 如果宽带绝热CP从质子到 碳/氮之后是第二个CP步骤，从‘3C到’5N或 5N到‘3C，选择感兴趣的’5N，‘3C对。 提高传输效率，绝热传输分布可以 在不损失补偿的情况下结合具体的CP方法 转移的选择性。这个实验是非常宽容的 考虑到所施加的射频场的大小和均匀性。 通常，直接CP的40%-60%的转移效率 (1H-GT；13C/15N)在200-500 MHz场中获得。我们已经应用了 建立偶极滤波或特殊CP技术 对侧链主链有用的二维关联 多肽(N-乙酰-缬氨酸、N-乙酰-精氨酸二水合物)的归属 和甲酰-MLF)。由于特定CP可以产生零量子或双量子 孤立的NH-CO、NH-CU主干对之间的一致性，这项技术 也可以用来确定局部主干扭转角 固态硬盘。对于光谱分配，另一种相关 实验(特定HETCOR)可能仅在特定情况下有用 间接检测维度中的光谱范围是所需的。在……里面 这个案子。载波频率可以通过的偏移步进 兴趣，从而减少了总的获取时间。我们的结果是 甲酰-MLF表明，特定CP的转移效率为 足以用于15N标记多肽的研究。这个 高转移效率还允许调查更大规模的 生物系统，我们已经成功地应用了特定的转移 研究26 kDa中Ala81-Arg82肽键的步骤 跨膜蛋白细菌视紫红质。因为七个人中只有一个 精氨酸残基直接与丙氨酸结合，13C标记 所有29个丙氨酸残基的羰基和氨基的15N标记 所有7个精氨酸残基的基团引入了独特的‘3C，15N对。 特异性CP实验显示Ala81-Arg82肽无序 在非选择性CP实验中被遮挡的键。这 蛋白质的不同状态会有不同的紊乱，尽管这种化学物质 班次变化很小。

A frequency selective heteronuclear polarization transfer technique is introduced for rotating solids. In this method, weak or medium strength radio frequency (rf) fields are applied to establish Hartmann-Hahn cross polarization that explicitly depends on the resonance offset of the involved nuclei. Under these conditions. SPECtrally Induced Filtering In Combination with Cross Polarization (SPECIFIC CP) can be achieved for spectral simplification or assignment purposes in heteronuclear spin pairs. Frequency selective transfer occurs if a broadband, adiabatic CP from protons to carbons/nitrogens is followed by a second CP step from '3C to '5N or 5N to '3C that selects the '5N, '3C pair of interest. To further enhance the transfer efficiency, an adiabatic transfer profile can be combined with the SPECIFIC CP approach without losing the offset selectivity of the transfer. The experiment is very forgiving with respect to the size and the homogeneity of the applied rf fields. Usually, transfer efficiencies of 40-60% of the direct CP (1H->13C/15N) are obtained at 200-500 MHz fields. We have applied the SPECIFIC CP technique to establish dipolar filtering or two-dimensional correlation useful for backbone of side-chain assignment in peptides (N-acetyl-valine, N-acetyl-arginine dihydrate and formyl-MLF). Since SPECIFIC CP can create zero- or double quantum coherence between isolated NH-CO, NH-CU backbone pairs, this technique can also be applied to determine local backbone torsion angles in the solid state. For spectral assignments, an alternative correlation experiment (SPECIFIC HETCOR) may be useful when only particular spectral ranges in the indirectly detected dimension are desired. In this case. the carrier frequency can be stepped through the offset of interest thereby reducing the total acquisition time. Our results for formyl-MLF indicate that the transfer efficiency of the SPECIFIC CP is sufficient for the investigations of 15N labeled polypeptides. The high transfer efficiency also permits the investigations of larger biological systems, and we have successfully applied SPECIFIC transfer steps to study the Ala8l-Arg82 peptide bond in the 26 kDa trans-membrane protein bacteriorhodopsin. Since only one of the seven arginine residues is directly bonded to alanine, 13C labeling of the carbonyls of all 29 alanine residues and 15N labeling of the amino groups of all 7 arginine residues introduces a unique '3C, 15N pair. The SPECIFIC CP experiment shows disorder in the Ala8l-Arg82 peptide bond that is obscured in the non-selective CP experiment. This disorder varies among states of the protein, although the chemical shift changes are small.