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首页> 外文期刊>Biochemistry >Ultrafast heme-residue bond formation in six-coordinate heme proteins: Implications for functional ligand exchange
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Ultrafast heme-residue bond formation in six-coordinate heme proteins: Implications for functional ligand exchange

机译：六坐标血红素蛋白中超快的血红素残基键形成：对功能性配体交换的影响

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摘要

A survey is presented of picosecond kinetics of heme-residue bond formation after photolysis of histidine, methionine, or cysteine, in a broad range of ferrous six-coordinate heme proteins. These include human neuroglobin, a bacterial heme-binding superoxide dismutase (SOD), plant cytochrome b(559), the insect nuclear receptor E75, horse heart cytochrome c and the heme domain of the bacterial sensor protein Dos. We demonstrate that the fastest and dominant phase of binding of amino acid residues to domed heme invariably takes place with a time constant in the narrow range of 5-7 ps. Remarkably, this is also the case in the heme-binding SOD, where the heme is solvent-exposed. We reason that this fast phase corresponds to barrierless formation of the heme-residue bond from a configuration close to the bound state. Only in proteins where functional ligand exchange occurs, additional slower rebinding takes place on the time scale of tens of picoseconds after residue dissociation. We propose that the presence of these slower phases reflects flexibility in the heme environment that allows external ligands (O-2, CO, NO,...) to functionally replace the internal residue after thermal dissociation of the heme-residue bond.
机译：在广泛的亚铁六配位血红素蛋白中，对组氨酸，蛋氨酸或半胱氨酸进行光解后，血红素-残基键形成的皮秒动力学研究已经完成。这些包括人神经球蛋白，细菌血红素结合超氧化物歧化酶（SOD），植物细胞色素b（559），昆虫核受体E75，马心脏细胞色素c和细菌传感器蛋白Dos的血红素结构域。我们证明，氨基酸残基与圆顶血红素结合的最快和显性阶段总是发生在5-7 ps的窄范围内的时间常数。显着地，在血红素结合的SOD中，血红素被溶剂暴露的情况也是如此。我们认为该快速相对应于从接近结合状态的构型无血红素-残基键的形成。仅在发生功能性配体交换的蛋白质中，残基解离后在数十皮秒的时间尺度上会发生更慢的重新结合。我们建议这些较慢的相的存在反映了血红素环境中的灵活性，允许外部配体（O-2，CO，NO，...）在血红素残基键热解离后功能上取代内部残基。

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