Contributions of the individual b subunits to the function of the peripheral stalk of F1F0 ATP synthase

• Main Author: Grabar, Tammy Weng Bohannon
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2004
• Subjects: Biochemistry; Molecular biology
• ISBN: 9780496037810; 0496037811

The universal molecule of biological energetics is adenosine triphosphate (ATP), and the enzyme involved in providing the majority of cellular ATP is F1F0 ATP synthase. Enzymes in this family utilize the electrochemical gradient of protons across membranes to synthesize ATP from ADP and inorganic phosphate in a coupled reaction. The cytoplasmic F 1 and the membrane-bound F0 sectors are linked by two stalk structures, the rotor stalk and the peripheral stalk. Proton conduction through the F0 sector drives the rotation of the rotor stalk within the catalytic core, which is held steadfast by the peripheral stalk. In Escherichia coli, the δ subunit of F1 and a parallel homodimer of identical b subunits constitute the peripheral stalk of F1F0 ATP synthase. Work accomplished in this dissertation indicates that the bacterial enzyme does not require two identical b subunits to form the dimer. Two different length b subunits, with a size difference of at least 14 amino acids, were capable of forming the b dimer of an intact F1 F0 ATP synthase complex. Also, in work presented in this dissertation, a defective mutation in one region of the b subunit was overcome by dimer formation with a second b subunit that contained defective mutation in a different region but had a wild-type sequence in the region of the former defective b subunit. This mutual complementation between fully defective b subunits indicated that each of the two b subunits makes a unique contribution to the functions of the peripheral stalk, such that one mutant b subunit is making up for what the other is lacking. Interestingly, the equivalent of the bacterial b subunit in plants exists as two genetically different subunits, and the mammal counterpart exists as at least four subunits. This work suggests that the individual functions of the b subunits may be reflected in the fact that higher organisms evolved to encode multiple b-type subunits.