Helix-Capping Histidines: Diversity of N鈥揌路路路N Hydrogen Bond Strength Revealed by 2hJNN Scalar Couplings

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• 作者：Matthew R. Preimesberger ; Ananya Majumdar ; Selena L. Rice ; Lauren Que ; Juliette T. J. Lecomte
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：November 24, 2015
• 年：2015
• 卷：54
• 期：46
• 页码：6896-6908
• 全文大小：682K
• ISSN：1520-4995

文摘

In addition to its well-known roles as an electrophile and general acid, the side chain of histidine often serves as a hydrogen bond (H-bond) acceptor. These H-bonds provide a convenient pH-dependent switch for local structure and functional motifs. In hundreds of instances, a histidine caps the N-terminus of 伪- and 3₁₀-helices by forming a backbone NH路路路N未1 H-bond. To characterize the resilience and dynamics of the histidine cap, we measured the trans H-bond scalar coupling constant, ^2hJ_NN, in several forms of Group 1 truncated hemoglobins and cytochrome b₅. The set of 19 measured ^2hJ_NN values were between 4.0 and 5.4 Hz, generally smaller than in nucleic acids (鈭?鈥?0 Hz) and indicative of longer, weaker bonds in the studied proteins. A positive linear correlation between ^2hJ_NN and the difference in imidazole ring ¹⁵N chemical shift (螖¹⁵N = |未¹⁵N未1 鈥?未¹⁵N蔚2|) was found to be consistent with variable H-bond length and variable cap population related to the ionization of histidine in the capping and noncapping states. The relative ease of ^2hJ_NN detection suggests that this parameter can become part of the standard arsenal for describing histidines in helix caps and other key structural and catalytic elements involving NH路路路N H-bonds. The combined nucleic acid and protein data extend the utility of ^2hJ_NN as a sensitive marker of local structural, dynamic, and thermodynamic properties in biomolecules.