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首页> 外文期刊>Journal of Molecular Biology >Effect of xenon binding to a hydrophobic cavity on the proton pumping cycle in bacteriorhodopsin.
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Effect of xenon binding to a hydrophobic cavity on the proton pumping cycle in bacteriorhodopsin.

机译：氙结合疏水腔对细菌视紫红质的质子泵浦周期的影响。

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摘要

To understand the functional role of apolar cavities in bacteriorhodopsin, a light-driven proton pump found in Halobacterium salinarum, we investigated the crystal structure in pressurized xenon or krypton. Diffraction data from the P622 crystal showed that one Xe or Kr atom binds to a preexisting hydrophobic cavity buried between helices C and D, located at the same depth from the membrane surface as Asp96, a key residue in the proton uptake pathway. The occupation fraction of Xe or Kr was calculated as approximately 0.32 at a pressure of 1 MPa. In the unphotolyzed state, the binding of Xe or Kr caused no large deformation of the cavity. However, the proton pumping cycle was greatly perturbed when an aqueous suspension of purple membrane was pressurized with xenon gas; that is, the decay of the M state was accelerated significantly (~5 times at full occupancy), while the decay of an equilibrium state of N and O was slightly decelerated. A similar but much smaller perturbation in the reaction kinetics was observed upon pressurization with krypton gas. In a glycerol/water mixture, xenon-induced acceleration of M decay became less significant in proportion to the water activity. Together with the structure of the xenon-bound protein, these observations suggest that xenon binding helps water molecules permeate into apolar cavities in the proton uptake pathway, thereby accelerating the water-mediated proton transfer from Asp96 to the Schiff base.
机译：为了了解非极性腔在细菌视紫红质中的作用，细菌视紫红质是在盐杆菌中发现的光驱动质子泵，我们研究了加压氙气或k气的晶体结构。来自P622晶体的衍射数据表明，一个Xe或Kr原子与埋在螺旋C和D之间的预先存在的疏水腔结合，该疏水腔距膜表面的深度与质子吸收途径中的关键残基Asp96相同。在1 MPa的压力下，Xe或Kr的占有率约为0.32。在未光解状态下，Xe或Kr的结合不会引起型腔的大变形。然而，当用氙气对紫色膜的水悬浮液加压时，质子泵的循环受到很大干扰。也就是说，M状态的衰减显着加速（在满时时约为5倍），而N和O平衡状态的衰减则稍有减速。用k气加压后，观察到反应动力学的类似但小得多的扰动。在甘油/水混合物中，氙诱导的M衰变的加速与水活度成比例的重要性降低。这些观察结果与氙结合蛋白的结构一起表明，氙的结合有助于水分子渗透到质子吸收途径中的非极性空穴中，从而加速了水介导的质子从Asp96到席夫碱的转移。

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