文章基本信息

标题：Interacting cytoplasmic loops of subunits a and c of Escherichia coli F1F0 ATP synthase gate H+ transport to the cytoplasm
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作者：P. Ryan Steed ; Kaitlin A. Kraft ; Robert H. Fillingame 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：47
页码：16730-16735
DOI：10.1073/pnas.1414660111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceH+ transport through the membrane-traversing F1F0 ATP synthase mechanically drives bond formation between ATP and Pi. For the enzyme in the inner membrane of Escherichia coli, we show here that the H+ transport pathway extends beyond the lipid bilayer into cytoplasmic loops connecting transmembrane helices in both subunits a and c of the transmembrane F0 sector. On the basis of chemical cross-linking, we postulate that the multiple loop regions functioning in H+ transport pack into a single domain, which then interacts with the cytoplasmic surface of the H+ channel within F0. The interaction of the loop regions with the H+ channel is proposed to specifically gate H+ release to the cytoplasmic side of the membrane during ATP synthesis. H+-transporting F1F0 ATP synthase catalyzes the synthesis of ATP via coupled rotary motors within F0 and F1. H+ transport at the subunit a-c interface in transmembranous F0 drives rotation of a cylindrical c10 oligomer within the membrane, which is coupled to rotation of subunit {gamma} within the 3{beta}3 sector of F1 to mechanically drive ATP synthesis. F1F0 functions in a reversible manner, with ATP hydrolysis driving H+ transport. ATP-driven H+ transport in a select group of cysteine mutants in subunits a and c is inhibited after chelation of Ag+ and/or Cd+2 with the substituted sulfhydryl groups. The H+ transport pathway mapped via these Ag+(Cd+2)-sensitive Cys extends from the transmembrane helices (TMHs) of subunits a and c into cytoplasmic loops connecting the TMHs, suggesting these loop regions could be involved in gating H+ release to the cytoplasm. Here, using select loop-region Cys from the single cytoplasmic loop of subunit c and multiple cytoplasmic loops of subunit a, we show that Cd+2 directly inhibits passive H+ transport mediated by F0 reconstituted in liposomes. Further, in extensions of previous studies, we show that the regions mediating passive H+ transport can be cross-linked to each other. We conclude that the loop-regions in subunits a and c that are implicated in H+ transport likely interact in a single structural domain, which then functions in gating H+ release to the cytoplasm.
关键词：F₁F₀ ATP synthase ; proton transport ; F₀ half channels ; gating mechanism ; F₀ a–c subunits