A reversible, H+-transporting ATPase catalyzes ATP synthesis during oxidative phosphorylation. The enzyme is made up of two sectors. F1 lies at the membrane surface, and on isolation catalyzes ATP hydrolysis. F-o extends through the membrane and functions in H+ transport. When the two sectors are properly coupled, ATP synthesis/hydrolysis is coupled to H+- translocation. The F1F-o complexes of mitochondria and Escherichia coli are very similar so general features of one system should be applicable to the other. In E. coli, F1 is composed of 3 pairs of alpha-beta subunits which form catalytic sites, and a single copy of the gamma, delta and epsilon subunits which link F1 to F-o. F-o is composed of 3 subunit types in an a1b2c10 ratio. Subunit c is thought to play a direct role in H+ transport, and in coupling H+ transport to ATP synthesis. It is a protein of 79 residues, folding in the membrane as a hairpin of two alpha-helices. Asp61 (centered in transmembrane helix-2) is thought to mediate H+ transport; H+ transport is thought to alter the loop region of subunit c and initiate a conformational change which ultimately promotes ATP release from alpha-beta subunits in Fl. We have shown that the essential carboxyl of subunit c can be moved from helix-2 to helix-1 and function retained. Analysis of suppressor mutants, optimizing function in the carboxyl-transposition mutant, led to identification of a transmembrane helical surface in subunit a that we now postulate interacts with subunit c. Secondly, polar loop mutants which uncouple H+-transport from ATP synthesis in F1 were characterized. Second site revertants to one of the uncoupled mutants map to a single residue of subunit epsilon. Here, we will better define, by both genetic and physical methods, the interaction between subunits c and a during H+ translocation, and the coupling interaction between the loop of subunit c and subunit epsilon. Additional aims include determination of the solvent accessibility and pKa of Asp6l in situ, and the relationship of this pKa to H+ binding during transport. We have shown that subunit c folds in a chloroform-methanol-H2O solvent much like it is predicted to fold in situ. Further, the unique chemical reactivity of Asp6l is retained. We have derived a low resolution model for the folding of subunit c in this solvent using 2D NMR methods and a novel approach using paramagnetic broadening with a nitroxide derivatived Asp6l. We propose to complete a high resolution solution structure by heteronuclear 3D and 4D methods and to test aspects of the solution model by mutagenesis. This structure will be compared to the structure in detergent micelles, and attempts made to study structural features of c-c and a-c aggregates in an organic solvent mixture. An understanding of structure-function relationships in membrane proteins is fundamental to many problems in biology and medicine. Few intrinsic proteins are understood in any detail. The H+ ATP synthase is central to all cellular functions, i.e. it makes the ATP. Abnormalities in the function of this enzyme, or other mitochondrial respiratory enzymes, result in human disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Method to Extend Research in Time (MERIT) Award (R37)
Project #
5R37GM023105-23
Application #
2734376
Study Section
Physical Biochemistry Study Section (PB)
Project Start
1976-05-01
Project End
1999-06-30
Budget Start
1998-07-01
Budget End
1999-06-30
Support Year
23
Fiscal Year
1998
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Biochemistry
Type
Schools of Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Fillingame, Robert H; Steed, P Ryan (2014) Half channels mediating H(+) transport and the mechanism of gating in the Fo sector of Escherichia coli F1Fo ATP synthase. Biochim Biophys Acta 1837:1063-8
Steed, P Ryan; Kraft, Kaitlin A; Fillingame, Robert H (2014) Interacting cytoplasmic loops of subunits a and c of Escherichia coli F1F0 ATP synthase gate H+ transport to the cytoplasm. Proc Natl Acad Sci U S A 111:16730-5
Steed, P Ryan; Fillingame, Robert H (2014) Residues in the polar loop of subunit c in Escherichia coli ATP synthase function in gating proton transport to the cytoplasm. J Biol Chem 289:2127-38
Moore, Kyle J; Fillingame, Robert H (2013) Obstruction of transmembrane helical movements in subunit a blocks proton pumping by F1Fo ATP synthase. J Biol Chem 288:25535-41
DeLeon-Rangel, Jessica; Ishmukhametov, Robert R; Jiang, Warren et al. (2013) Interactions between subunits a and b in the rotary ATP synthase as determined by cross-linking. FEBS Lett 587:892-7
Uhlemann, Eva-Maria E; Pierson, Hannah E; Fillingame, Robert H et al. (2012) Cell-free synthesis of membrane subunits of ATP synthase in phospholipid bicelles: NMR shows subunit a fold similar to the protein in the cell membrane. Protein Sci 21:279-88
Dong, Hui; Fillingame, Robert H (2010) Chemical reactivities of cysteine substitutions in subunit a of ATP synthase define residues gating H+ transport from each side of the membrane. J Biol Chem 285:39811-8
Steed, P Ryan; Fillingame, Robert H (2009) Aqueous accessibility to the transmembrane regions of subunit c of the Escherichia coli F1F0 ATP synthase. J Biol Chem 284:23243-50
Moore, Kyle J; Angevine, Christine M; Vincent, Owen D et al. (2008) The cytoplasmic loops of subunit a of Escherichia coli ATP synthase may participate in the proton translocating mechanism. J Biol Chem 283:13044-52
Moore, Kyle J; Fillingame, Robert H (2008) Structural interactions between transmembrane helices 4 and 5 of subunit a and the subunit c ring of Escherichia coli ATP synthase. J Biol Chem 283:31726-35

Showing the most recent 10 out of 70 publications