Distinct Differences in Structural States of Conserved Histidines in Two Related Proteins: NMR Studies of the Chemokines CXCL1 and CXCL8 in the Free Form and Macromolecular Complexes.
Distinct Differences in Structural States of Conserved Histidines in Two Related Proteins: NMR Studies of the Chemokines CXCL1 and CXCL8 in the Free Form and Macromolecular Complexes.
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两种相关蛋白质中保守组氨酸结构状态的明显差异：游离形式和大分子复合物中趋化因子 CXCL1 和 CXCL8 的 NMR 研究。
DOI：
10.1021/acs.biochem.8b00756
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发表时间：
2018
期刊：
影响因子：
2.9
通讯作者：
Rajarathnam,Krishna
中科院分区：
文献类型：
--
作者：
Sepuru,KrishnaMohan;Rajarathnam,Krishna
氢键和离子相互作用在大分子识别和功能中起着重要作用。与赖氨酸和组氨酸不同，组氨酸如何介导这些相互作用还不太清楚，这是由于其侧链咪唑的独特性质，包括具有两个可滴定氮的芳香环，可以显著变化的pKa，以及以三种不同形式存在的能力：质子化咪唑和两种互变异构中性（Nδ 1和Nε2）状态。在这里，我们的特点是组氨酸的结构特征的趋化因子CXCL 8和CXCL 1在自由，GAG肝素结合，CXCR 2受体N-末端结构域结合状态，使用溶液NMR光谱。CXCL 8和CXCL 1共有两个保守的组氨酸，一个在N环中，另一个在30 s环中。在CXCL 8中，两种组氨酸均以Nε 2互变异构体状态以游离、GAG结合和受体结合形式存在。另一方面，在未配体的CXCL 1中，两个组氨酸中的每一个以两种状态存在，作为中性Nε 2互变异构体和带电咪唑鎓。此外，两种组氨酸在GAG结合形式中仅以咪唑鎓存在，在受体结合形式中仅以Nε 2互变异构体存在。两种趋化因子中的N-环组氨酸单独参与直接GAG和受体相互作用，表明30 s环的作用在趋化因子之间变化。我们的观察，保守的组氨酸的结构特征和它们在两个相关蛋白质的功能作用可以是完全不同的是新的。我们进一步提出，直接探测咪唑的结构特征是必不可少的，以充分了解组氨酸功能的分子基础。
Hydrogen-bonding and ionic interactions play fundamental roles in macromolecular recognition and function. In contrast to lysines and arginines, how histidines mediate these interactions is less well-understood due to the unique properties of its side chain imidazole that include an aromatic ring with two titratable nitrogens, a pKathat can vary significantly, and the ability to exist in three distinct forms: protonated imidazolium and two tautomeric neutral (Nδ1and Nε2) states. Here, we characterized the structural features of histidines in the chemokines CXCL8 and CXCL1 in the free, GAG heparin-bound, and CXCR2 receptor N-terminal domain-bound states using solution NMR spectroscopy. CXCL8 and CXCL1 share two conserved histidines, one in the N-loop and the other in the 30s loop. In CXCL8, both histidines exist in the Nε2tautomeric state in the free, GAG-bound, and receptor-bound forms. On the other hand, in unliganded CXCL1, each of the two histidines exists in two states, as the neutral Nε2tautomer and charged imidazolium. Further, both histidines exclusively exist as the imidazolium in the GAG-bound and as the Nε2tautomer in the receptor-bound forms. The N-loop histidine alone in both chemokines is involved in direct GAG and receptor interactions, indicating the role of the 30s loop varies between the chemokines. Our observation that the structural features of conserved histidines and their functional role in two related proteins can be quite different is novel. We further propose that directly probing the imidazole structural features is essential to fully appreciate the molecular basis of histidine function.