ESEEM studies of peptide nitrogen hyperfine coupling in tyrosyl radicals and model peptides.
ESEEM studies of peptide nitrogen hyperfine coupling in tyrosyl radicals and model peptides.
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酪氨酰自由基和模型肽中肽氮超精细耦合的 ESEEM 研究。
DOI：
10.1021/jp071402x
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Barry,BridgetteA
中科院分区：
文献类型：
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作者：
McCracken,John;Vassiliev,IlyaR;Yang,En-Che;Range,Kevin;Barry,BridgetteA
酪氨酸自由基在多种酶的远程电子转移中起重要作用，但控制中点电位和电子转移速率的蛋白质环境因素尚不清楚。为了更详细地了解蛋白质序列的影响，我们通过紫外光解对多晶酪氨酸及其15n标记同位素体中产生的酪氨酸自由基进行了14n和15n电子自旋回波包络调制（ESEEM）测量。对含酪氨酸五肽样品中产生的酪氨酸自由基进行14N-ESEEM检测。模拟14n -和15n -酪氨酸自由基的ESEEM测量结果显示，胺或酰胺氮没有明显的各向同性超细分裂；各向异性氮超细耦合幅值（0.21 MHz）与偶极子-偶极子距离3.0 Å一致。利用密度泛函理论计算了四种不同酪氨酸自由基构象中氨基氮与各向同性和各向异性的超精细耦合。与模拟数据的比较表明，在pH为11时，酪氨酸生成的能量最低的自由基构象具有76°C - α - Cβ - C1 ‘ - c2 ’环和- 73°C - Cα - Cβ - C1 '主二面角。此外，通过对酪氨酸自由基14n - eseem的分析，得到了核四极耦合张量的大小、取向和不对称性。模拟结果表明，酪氨酸和五肽样品在核四极张量的耦合和取向上存在差异。这些结果表明，序列或构象诱导不同酪氨酸肽中NH键离子特性的变化。
Tyrosyl radicals are important in long-range electron transfer in several enzymes, but the protein environmental factors that control midpoint potential and electron transfer rate are not well understood. To develop a more detailed understanding of the effect of protein sequence, we have performed14N and15N electron spin echo envelope modulation (ESEEM) measurements on tyrosyl radical, generated either in polycrystalline tyrosinate or in its15N-labeled isotopomer, by UV photolysis.14N-ESEEM was also performed on tyrosyl radical generated in tyrosine-containing pentapeptide samples. Simulation of the14N- and15N-tyrosyl radical ESEEM measurements yielded no significant isotropic hyperfine splitting to the amine or amide nitrogen; the amplitude of the anisotropic, nitrogen hyperfine coupling (0.21 MHz) was consistent with a dipole−dipole distance of 3.0 Å. Density functional theory was used to calculate the isotropic and anisotropic hyperfine couplings to the amino nitrogen in four different tyrosyl radical conformers. Comparison with the simulated data suggested that the lowest energy radical conformer, generated in tyrosine at pH 11, has a 76° Cα−Cβ−C1‘−C2‘ring and a −73° C−Cα−Cβ−C1‘backbone dihedral angle. In addition, the magnitude, orientation, and asymmetry of the nuclear quadrupole coupling tensor were derived from analysis of the tyrosyl radical14N-ESEEM. The simulations showed differences in the coupling and orientation of the nuclear quadrupole tensor, when the tyrosinate and pentapeptide samples were compared. These results suggest sequence- or conformation-induced changes in the ionic character of the NH bond in different tyrosine-containing peptides.