Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem 91904, Israel.
Proc Natl Acad Sci U S A. 2014 Mar 18;111(11):4085-90. doi: 10.1073/pnas.1319827111. Epub 2014 Mar 3.
Macromolecules are characterized by their particular arrangement of H bonds. Many of these interactions involve a single donor and acceptor pair, such as the regular H-bonding pattern between carbonyl oxygens and amide H(+)s four residues apart in α-helices. The H-bonding potential of some acceptors, however, leads to the phenomenon of overcoordination between two donors and one acceptor. Herein, using isotope-edited Fourier transform infrared measurements and density functional theory (DFT) calculations, we measured the strength of such bifurcated H bonds in a transmembrane α-helix. Frequency shifts of the (13)C=(18)O amide I mode were used as a reporter of the strength of the bifurcated H bond from a thiol and hydroxyl H(+) at residue i + 4. DFT calculations yielded very similar frequency shifts and an energy of -2.6 and -3.4 kcal/mol for the thiol and hydroxyl bifurcated H bonds, respectively. The strength of the intrahelical bifurcated H bond is consistent with its prevalence in hydrophobic environments and is shown to significantly impact side-chain rotamer distribution.
大分子的特点是其氢键的特殊排列。这些相互作用中有许多涉及单个供体和受体对，例如在α-螺旋中相隔四个残基的羰基氧和酰胺 H(+)之间的规则氢键模式。然而，一些受体的氢键结合能力导致了两个供体和一个受体之间的过度配位现象。在此，我们使用同位素编辑傅里叶变换红外测量和密度泛函理论 (DFT) 计算测量了跨膜α-螺旋中这种分叉氢键的强度。(13)C=(18)O 酰胺 I 模式的频率位移被用作来自残基 i + 4 的巯基和羟基 H(+)的分叉氢键强度的报告。DFT 计算得到了非常相似的频率位移，并且对于巯基和羟基分叉氢键，能量分别为-2.6 和-3.4 kcal/mol。腔内分叉氢键的强度与其在疏水环境中的普遍性一致，并显示出对侧链旋转异构体分布有显著影响。
