Department of Chemistry, University of California Davis, Davis, California 95616, United States.
J Am Chem Soc. 2011 Nov 16;133(45):18098-101. doi: 10.1021/ja208462t. Epub 2011 Oct 25.
Redox-active tryptophans are important in biological electron transfer and redox biochemistry. Proteins can tune the electron transfer kinetics and redox potentials of tryptophan via control of the protonation state and the hydrogen-bond strength. We examine the local environment of two neutral tryptophan radicals (Trp108 on the solvent-exposed surface and Trp48 buried in the hydrophobic core) in two azurin variants. Ultrahigh-field EPR spectroscopy at 700 GHz and 25 T allowed complete resolution of all of the principal components of the g tensors of the two radicals and revealed significant differences in the g tensor anisotropies. The spectra together with (2)H ENDOR spectra and supporting DFT calculations show that the g tensor anisotropy is directly diagnostic of the presence or absence as well as the strength of a hydrogen bond to the indole nitrogen. The approach is a powerful one for identifying and characterizing hydrogen bonds that are critical in the regulation of tryptophan-assisted electron transfer and tryptophan-mediated redox chemistry in proteins.
氧化还原活性色氨酸在生物电子转移和氧化还原生物化学中很重要。蛋白质可以通过控制质子化状态和氢键强度来调节色氨酸的电子转移动力学和氧化还原电位。我们研究了两种天青蛋白变体中两个中性色氨酸自由基（溶剂暴露表面上的 Trp108 和埋藏在疏水性核心中的 Trp48）的局部环境。在 700GHz 和 25T 的超高场 EPR 光谱下，两个自由基的 g 张量的所有主分量都可以完全分辨出来，并显示出 g 张量各向异性的显著差异。这些光谱与（2）H ENDOR 光谱和支持的 DFT 计算一起表明，g 张量各向异性直接可以诊断出与吲哚氮的氢键的存在、不存在以及强度。这种方法是一种强大的方法，可用于识别和表征在调节色氨酸辅助电子转移和蛋白质中色氨酸介导的氧化还原化学中至关重要的氢键。
