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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Aqueous access pathways in subunit a of rotary ATP synthase extend to both sides of the membrane
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Aqueous access pathways in subunit a of rotary ATP synthase extend to both sides of the membrane

机译：旋转ATP合酶亚基a中的水通道延伸到膜的两侧

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摘要

The role of subunit a in promoting proton translocation and rotary motion in the Escherichia coli F_1F_0 ATP synthase is poorly understood. In the membrane-bound F_0 sector of the enzyme, H~+ binding and release occur at Asp-61 in the middle of the second transmembrane helix (TMH) of subunit c. Protons are thought to reach Asp-61 at the center of the membrane via aqueous channels formed at least in part by one or more of the five TMHs of subunit a. Aqueous access pathways have previously been mapped to surfaces of aTMH4. Here we have substituted Cys into the second and fifth TMHs of subunit a and carried out chemical modification with Ag~+ and N-ethylmaleim-ide to define the aqueous accessibility of residues along these helices. Access to cAsp-61 at the center of the membrane may be mediated in part by Ag~+-sensitive residues 248, 249, 251, and 252 in aTMH5. From the periplasmic surface, aqueous access to cAsp-61 may be mediated by silver-sensitive residues 115, 116, 119, 120, 122, and 126 in aTMH2. The Ag~+-sensitive residues in TMH2, -4, and -5 form a continuum extending from the periplasmic to the cytoplasmic side of the membrane. In an arrangement of helices supported by second-site revertant and crosslinking analyses, these residues cluster at the interior of a four-helix bundle formed by TMH2-5. The aqueous access pathways at the interior of subunit a may be gated by a swiveling of helices in this bundle, alternately exposing cytoplasmic and periplasmic half channels to cAsp-61 during the H~+ transport cycle.
机译：对亚单位a在促进大肠杆菌F_1F_0 ATP合酶中质子易位和旋转运动中的作用了解甚少。在酶的膜结合F_0区段中，H +结合和释放发生在亚基c的第二个跨膜螺旋（TMH）中间的Asp-61处。质子被认为经由至少部分地由亚基a的五个TMH中的一个或多个形成的水性通道到达膜中心的Asp-61。水性通路先前已被映射到aTMH4的表面。在这里，我们将Cys取代为亚基a的第二个和第五个TMHs，并用Ag〜+和N-乙基马来酰亚胺进行化学修饰，以定义沿这些螺旋残基的水可及性。膜中央对cAsp-61的进入可能部分由aTMH5中的Ag +敏感残基248、249、251和252介导。在aTMH2中，银质敏感的残基115、116、119、120、122和126可以从周质表面介导水进入cAsp-61。 TMH2，-4和-5中的Ag〜+敏感残基形成从膜的周质侧延伸到细胞质侧的连续体。在第二点还原剂和交联分析支持的螺旋排列中，这些残基聚集在TMH2-5形成的四螺旋束的内部。可以通过在该束中旋转螺旋来控制亚基a内部的水通道，在H +转运周期中交替将胞质和周质半通道暴露于cAsp-61。

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