The physiological role of proteins is frequently linked to interactions with non-protein ligands or posttranslational modifications. Structural characterization of these complexes or modified proteins by NMR may be difficult as the ligands are usually not available in an isotope-labeled form and NMR spectra may suffer from signal overlap. Here, we present an optimized approach that uses specific NMR isotope-labeling schemes for overcoming both hurdles. This approach enabled the high-resolution structure determination of the farnesylated C-terminal domain of the peroxisomal protein PEX19. The approach combines specific 13C, 15N and 2H isotope labeling with tailored NMR experiments to (i) unambiguously identify the NMR frequencies and the stereochemistry of the unlabeled 15-carbon isoprenoid, (ii) resolve the NMR signals of protein methyl groups that contact the farnesyl moiety and (iii) enable the unambiguous assignment of a large number of protein-farnesyl NOEs. Protein deuteration was combined with selective isotope-labeling and protonation of amino acids and methyl groups to resolve ambiguities for key residues that contact the farnesyl group. Sidechain-labeling of leucines, isoleucines, methionines, and phenylalanines, reduced spectral overlap, facilitated assignments and yielded high quality NOE correlations to the unlabeled farnesyl. This approach was crucial to enable the first NMR structure of a farnesylated protein. The approach is readily applicable for NMR structural analysis of a wide range of protein-ligand complexes, where isotope-labeling of ligands is not well feasible.

中文翻译：

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具有未标记配体的复合物中蛋白质的NMR结构测定的选择性同位素标记。

蛋白质的生理作用通常与与非蛋白质配体的相互作用或翻译后修饰有关。这些配体或修饰蛋白的NMR结构表征可能很困难，因为配体通常无法以同位素标记的形式获得，并且NMR谱图可能会出现信号重叠。在这里，我们提出了一种优化的方法，该方法使用特定的NMR同位素标记方案来克服这两个障碍。这种方法使过氧化物酶体蛋白PEX19的法呢基化的C末端结构域的高分辨率结构确定。该方法将特定的13C，15N和2H同位素标记与量身定制的NMR实验结合在一起，以（i）明确确定未标记的15碳类异戊二烯的NMR频率和立体化学，（ii）解析与法呢基部分接触的蛋白质甲基的NMR信号，以及（iii）能够明确分配大量蛋白质-法呢基NOE。蛋白质氘与选择性同位素标记和氨基酸和甲基质子化相结合，以解决与法呢基接触的关键残基的歧义。亮氨酸，异亮氨酸，蛋氨酸和苯丙氨酸的侧链标记，减少光谱重叠，促进分配并产生与未标记法呢基的高质量NOE相关性。该方法对于实现法呢基化蛋白质的首个NMR结构至关重要。该方法很容易适用于各种蛋白质-配体配合物的NMR结构分析，而配体的同位素标记不太可行。