Arg302 控制 LacY 中 Glu325 的 pK 值。
Arg302 governs the pK of Glu325 in LacY.
机构信息
Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, Chimie de la Matière Complexe (CMC), Université de Strasbourg, CNRS, 67081 Strasbourg, France.
Department of Physiology, University of California, Los Angeles, CA 90095-7327.
出版信息
Proc Natl Acad Sci U S A. 2019 Mar 12;116(11):4934-4939. doi: 10.1073/pnas.1820744116. Epub 2019 Feb 21.
Lactose permease is a paradigm for the major facilitator superfamily, the largest family of ion-coupled membrane transport proteins known at present. LacY carries out the coupled stoichiometric symport of a galactoside with an H, using the free energy released from downhill translocation of H to drive accumulation of galactosides against a concentration gradient. In neutrophilic , internal pH is kept at ∼7.6 over the physiological range, but the apparent pK (pK) for galactoside binding is 10.5. Surface-enhanced infrared absorption spectroscopy (SEIRAS) demonstrates that the high pK is due to Glu325 (helix X), which must be protonated for LacY to bind galactoside effectively. Deprotonation is also obligatory for turnover, however. Here, we utilize SEIRAS to study the effect of mutating residues in the immediate vicinity of Glu325 on its pK The results are consistent with the idea that Arg302 (helix IX) is important for deprotonation of Glu325.
乳糖渗透酶是主要易化子超家族的典范，是目前已知的最大的离子偶联膜转运蛋白家族。 LacY 进行半乳糖苷与 H 的偶联计量协同转运，利用 H 的向下转运释放的自由能驱动半乳糖苷的积累，以对抗浓度梯度。在嗜中性粒细胞中，生理范围内的内部 pH 值保持在约 7.6，但半乳糖苷结合的表观 pK（pK）为 10.5。表面增强红外吸收光谱（SEIRAS）表明，高 pK 值是由于 Glu325（X 螺旋），LacY 必须质子化才能有效地结合半乳糖苷。然而，去质子化对于周转率也是必需的。在这里，我们利用 SEIRAS 研究了紧邻 Glu325 的残基突变对其 pK 的影响。结果与 Arg302（IX 螺旋）对 Glu325 去质子化很重要的观点一致。
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