SPECIFIC CP ASSIGNMENT & SPECTRAL SIMPLIFICATION IN HETERONUCLEAR SPIN SYSTEM

一种频率选择性异向极化传输 技术介绍了旋转固体。 在这种方法中，弱或 施加中等强度的射频（RF）场 Hartmann-Hahn交叉极化，明确地取决于 所涉及的原子核的共振偏移。 在这种情况下。 与交叉极化相结合的光谱诱导滤波 （特定CP）可用于频谱简化或 在异序自旋对中的分配目的。 频率选择性 如果从质子到质子的宽带绝热CP发生转移， 碳/氮之后是从“3C”到“5 N”的第二CP步骤，或者 5 N到'3C，选择感兴趣的' 5 N，'3C对。 进一步 为了提高传递效率，可以 与SPECIFIC CP方法相结合，而不会丢失偏移 转移的选择性。 实验是非常宽容的， 关于所施加的RF场的大小和均匀性。 通常，直接CP的40-60%的转移效率 (1H->13C/15N）。 我们已经应用了 建立偶极滤波的特定CP技术或 用于侧链骨架的二维相关性 肽中的分配（N-乙酰基-缬氨酸、N-乙酰基-精氨酸二水合物 和甲酰基-MLF）。 由于特定CP可以创建零量子或双量子 分离的NH-CO、NH-CU主链对之间的相干性，该技术 也可以应用于确定局部骨干扭转角 固体状态。 对于光谱分配，另一种相关性 实验（特定HETCOR）可能是有用的，当只有特定的 期望间接检测维度中的光谱范围。 在 这个案子 载波频率可以步进通过 从而减少了总的采集时间。 我们的结果 甲酰基-MLF表明特异性CP的转移效率是 足以研究15 N标记的多肽。 的 高转移效率还允许研究更大的 生物系统，我们已经成功地应用了特定的转移 研究26 kDa中Ala 81-Arg 82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键合， 所有29个丙氨酸残基的羰基和氨基的15 N标记 所有7个精氨酸残基的基团引入独特的“3C，15 N对。 特异性CP实验显示Ala 81-Arg 82肽中的紊乱 在非选择性CP实验中被遮蔽的键。 这 蛋白质的状态之间的紊乱是不同的，尽管化学物质 班次变化不大。

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.