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：2001
卷号：98
期号：12
页码：6560-6564
DOI：10.1073/pnas.111128098
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The F1F0 ATP synthase is the smallest motor enzyme known. Previous studies had established that the central stalk, made of the {gamma} and {varepsilon} subunits in the F1 part and c subunit ring in the F0 part, rotates relative to a stator composed of 3{beta}3{delta}ab2 during ATP hydrolysis and synthesis. How this rotation is regulated has been less clear. Here, we show that the {varepsilon} subunit plays a key role by acting as a switch of this motor. Two different arrangements of the {varepsilon} subunit have been visualized recently. The first has been observed in beef heart mitochondrial F1-ATPase where the C-terminal portion is arranged as a two--helix hairpin structure that extends away from the 3{beta}3 region, and toward the position of the c subunit ring in the intact F1F0. The second arrangement was observed in a structure determination of a complex of the {gamma} and {varepsilon} subunits of the Escherichia coli F1-ATPase. In this, the two C-terminal helices are apart and extend along the {gamma} to interact with the and {beta} subunits in the intact complex. We have been able to trap these two arrangements by cross-linking after introducing appropriate Cys residues in E. coli F1F0, confirming that both conformations of the {varepsilon} subunit exist in the enzyme complex. With the C-terminal domain of {varepsilon} toward the F0, ATP hydrolysis is activated, but the enzyme is fully coupled in both ATP hydrolysis and synthesis. With the C-terminal domain toward the F1 part, ATP hydrolysis is inhibited and yet the enzyme is fully functional in ATP synthesis; i.e., it works in one direction only. These results help explain the inhibitory action of the {varepsilon} subunit in the F1F0 complex and argue for a ratchet function of this subunit.
