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首页> 外文期刊>Biochemistry >Protonation behavior of histidine 24 and histidine 119 in forming the pH 4 folding intermediate of apomyoglobin
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Protonation behavior of histidine 24 and histidine 119 in forming the pH 4 folding intermediate of apomyoglobin

机译：组氨酸24和组氨酸119的质子化行为形成磷肌红蛋白的pH 4折叠中间体

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Heteronuclear NMR methods are used to study the protonation of histidine and aspartate residues in the acid-induced unfolding of recombinant sperm whale apomyoglobin. The results are combined with fluorescence and circular dichroism measurements of acid-induced unfolding of wild-type and double mutant (H24V/H119F) proteins. They are consistent with a simple model in which the failure to protonate a single buried histidine, H24, is largely responsible for the partial unfolding of native (N) wild-type apomyoglobin to the pH 4 folding intermediate (T), H24 is known to form an unusual interaction in which its side chain is buried and hydrogen-bonded to the side chain of H119, Two-dimensional H-1-N-15 heteronuclear NMR spectra indicate that H24 is present in the rare delta tautomeric farm and remains neutral until N unfolds to I, while H119 becomes protonated before the N --> I reaction occurs. In the H24V/H119F double mutant, all histidines are protonated in N and the N --> I reaction occurs at lower pH. Therefore, the protonation of aspartate and/or glutamate residues must provide an additional driving force for the N to I reaction, Two-dimensional H-1-C-13 NMR experiments are used to measure the protonation of aspartates in selectively C-13-labeled apomyoglobin; the results indicate that none of the aspartate residues has a strongly depressed pK(a) in N, as would be expected if it forms a stabilizing salt bridge. [References: 48]
机译：异核NMR方法用于研究酸诱导的重组抹香鲸脂球蛋白解折叠中组氨酸和天冬氨酸残基的质子化。该结果与荧光诱导的野生型和双突变（H24V / H119F）蛋白的解折叠的荧光和圆二色性测量相结合。它们与一个简单的模型一致，在该模型中，无法对单个掩埋的组氨酸H24进行质子化是造成天然（N）野生型载脂蛋白向pH 4折叠中间体（T）部分解折叠的主要原因。形成一个不寻常的相互作用，其中其侧链被掩埋并氢键合到H119的侧链上，二维H-1-N-15异核NMR光谱表明，H24存在于罕见的三角互变异构场中，并保持中性直至N向I展开，而H119在N-> I反应发生之前被质子化。在H24V / H119F双突变体中，所有组氨酸均在N中被质子化，N→I反应在较低的pH值下发生。因此，天冬氨酸和/或谷氨酸残基的质子化必须为N对I反应提供额外的驱动力。二维H-1-C-13 NMR实验用于测量选择性C-13-中天冬氨酸的质子化标记的肌红蛋白;结果表明，天冬氨酸残基中没有一个在N中强烈抑制pK（a），如形成稳定的盐桥所预期的那样。 [参考：48]

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