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首页> 外文期刊>Biophysical Chemistry: An International Journal Devoted to the Physical Chemistry of Biological Phenomena >Structural and thermodynamic aspects of cooperativity in the homodimeric hemoglobin from Scapharca inaequivalvis.
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Structural and thermodynamic aspects of cooperativity in the homodimeric hemoglobin from Scapharca inaequivalvis.

机译：Scapharca inaequivalvis的同型二聚体血红蛋白中协同作用的结构和热力学方面。

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摘要

The homodimeric cooperative hemoglobin from the mollusk Scapharca inaequivalvis displays an unusual subunit assembly with respect to vertebrate hemoglobins. The intersubunit contact region is formed by the two heme-carrying E and F helices, which bring the two hemes in contact with each other. At variance with tetrameric vertebrate hemoglobins, the ligand binding is not accompanied by a significant quaternary transition. The major ligand-linked changes are tertiary and are limited to the heme pocket and subunit interface. These unique structural features of HbI are not easily reconciled with the classical thermodynamic models used to describe cooperative ligand binding in vertebrate hemoglobins. The lack of distinct quaternary states and the absence of allosteric effectors suggested that cooperativity in HbI is entirely homotropic in origin. Thereafter, high resolution X-ray crystallographic data displayed the preferential binding of water molecules at the intersubunit interface in the unliganded protein with respect to the liganded one. These ordered water molecules were thus proposed to act as heterotropic effectors in HbI. The contribution of specific water binding to the observed cooperativity in HbI is discussed in the framework of the enthalpy-entropy compensation effect emerging from previous accurate equilibrium oxygen binding measurements.
机译：来自软体动物Scapharca inaequivalvis的同型二聚体合作血红蛋白相对于脊椎动物血红蛋白表现出不同寻常的亚基组装。亚基间接触区域由两个携带血红素的E和F螺旋形成，这两个使两个血红素彼此接触。与四聚体脊椎动物血红蛋白不同，配体结合不伴随显着的四元过渡。主要的配体连接变化是三级的，并且限于血红素囊和亚基界面。 HbI的这些独特的结构特征不容易与用于描述脊椎动物血红蛋白中协同配体结合的经典热力学模型相一致。缺乏明显的四元态和缺乏变构效应子表明，HbI中的合作性在起源上完全是同质的。此后，高分辨率的X射线晶体学数据显示了水分子在未配体蛋白质的亚基界面处相对于配体的优先结合。因此，提出了这些有序的水分子在HbI中起异质效应作用。在先前精确的平衡氧结合测量中产生的焓-熵补偿效应的框架中讨论了特定水结合对HbI中观察到的协同性的贡献。

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