Biophysical properties of a c-type heme in chemotaxis signal transducer protein DcrA.
Biophysical properties of a c-type heme in chemotaxis signal transducer protein DcrA.
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DOI：
10.1021/bi0513352
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发表时间：
2005-11
期刊：
影响因子：
2.9
通讯作者：
S. Yoshioka;Katsuaki Kobayashi;Hideaki Yoshimura;T. Uchida;T. Kitagawa;S. Aono
中科院分区：
文献类型：
--
作者：
S. Yoshioka;Katsuaki Kobayashi;Hideaki Yoshimura;T. Uchida;T. Kitagawa;S. Aono
来自硫酸盐还原菌脱硫弧菌Hildenborough的趋化性信号转导蛋白DcrA先前显示在其周质结构域（DcrA-N）中含有c型血红素，用于感测氧化还原和/或氧[Fu等人（1994）J. Bacteriol. 176，344-350]，其是含有C型血红素作为辅基的基于血红素的传感器蛋白的第一个实例。光学吸收和共振拉曼光谱表明DcrA-N中的血红素c表现出氧化还原依赖的配体交换。在还原时，可能是铁血红素c的第六配体的水分子被内源性氨基酸取代。尽管DcrA-N中的还原血红素与两个内源性轴向配体是六配位的，但CO可以容易地结合到还原血红素以形成CO结合的DcrA-N。还原的DcrA-N与分子氧的反应导致自氧化以形成三价铁状态，而不形成任何稳定的氧结合形式，这可能是由于DcrA-N的极低氧化还原电位（~ 250 mV）。我们的研究支持Fu等人的最初想法，即DcrA将作为氧化还原和/或氧传感器，其中水和内源性氨基酸之间的配体交换是信号转导的触发器。虽然与其他血红素蛋白相比，CO对DcrA-N的亲和力（Kd = 138 microM）显着较弱，但我们认为CO可能是另一种生理效应分子。
Chemotaxis signal transducer protein DcrA from a sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough was previously shown to contain a c-type heme in its periplasmic domain (DcrA-N) for sensing redox and/or oxygen [Fu et al. (1994) J. Bacteriol. 176, 344-350], which is the first example of a heme-based sensor protein containing a c-type heme as a prosthetic group. Optical absorption and resonance Raman spectroscopies indicates that heme c in DcrA-N shows a redox-dependent ligand exchange. Upon reduction, a water molecule that may be the sixth ligand of the ferric heme c is replaced by an endogenous amino acid. Although the reduced heme in DcrA-N is six-coordinated with two endogenous axial ligands, CO can easily bind to the reduced heme to form CO-bound DcrA-N. Reaction of the reduced DcrA-N with molecular oxygen results in autoxidation to form a ferric state without forming any stable oxygen-bound form probably due to the extremely low redox potential of DcrA-N (-250 mV). Our study supports the initial idea by Fu et al. that DcrA would act as a redox and/or oxygen sensor, in which the ligand exchange between water and an endogenous amino acid is a trigger for signal transduction. While the affinity of CO to DcrA-N (Kd = 138 microM) is significantly weak compared to those of other heme proteins, we suggest that CO might be another physiological effector molecule.