Fluidity of structure and swiveling of helices in the subunit c ring of Escherichia coli ATP synthase as revealed by cysteine-cysteine cross-linking.
Subunit c in the membrane-traversing F(0) sector of Escherichia coli ATP synthase is known to fold with two transmembrane helices and form an oligomeric ring of 10 or more subunits in the membrane. Models for the E. coli ring structure have been proposed based upon NMR solution structures and intersubunit cross-linking of Cys residues in the membrane. The E. coli models differ from the recent x-ray diffraction structure of the isolated Ilyobacter tartaricus c-ring. Furthermore, key cross-linking results supporting the E. coli model prove to be incompatible with the I. tartaricus structure. To test the applicability of the I. tartaricus model to the E. coli c-ring, we compared the cross-linking of a pair of doubly Cys substituted c-subunits, each of which was compatible with one model but not the other. The key finding of this study is that both A21C/M65C and A21C/I66C doubly substituted c-subunits form high yield oligomeric structures, c(2), c(3)... c(10), via intersubunit disulfide bond formation. The results indicate that helical swiveling, with resultant interconversion of the two conformers predicted by the E. coli and I. tartaricus models, must be occurring over the time course of the cross-linking experiment. In the additional experiments reported here, we tried to ascertain the preferred conformation in the membrane to help define the most likely structural model. We conclude that both structures must be able to form in the membrane, but that the helical swiveling that promotes their interconversion may not be necessary during rotary function.
Vincent
Owen D
OD
Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706.
Schwem
Brian E
BE
Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706.
Steed
P Ryan
PR
Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706.
Jiang
Warren
W
Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706.
Fillingame
Robert H
RH
Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706. Electronic address: rhfillin@wisc.edu.
D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D003300:Copper / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008958:Models, Molecular; D008968:Molecular Conformation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D006180:Proton-Translocating ATPases / Q000378:metabolism / Q000502:physiology*; D014961:X-Ray Diffraction
D003432:Cross-Linking Reagents; D003300:Copper; D006180:Proton-Translocating ATPases; D003545:Cysteine