(20). The obvious asymmetric positioning of the coiled coil of the y subunit is a key

feature to the mechanics of the binding change mechanism of F1Fo ATP synthase. Its

large carboxyl terminus a-helix passes through a hydrophobic sleeve formed by six

proline-rich loops of the a and P subunits, undoubtingly resulting in the conformational

changes occurring in the catalytic sites (20). In the PE Subunit (see above), several

hydrogen bonds are formed with the y subunit, which forms a "catch", resulting in

conformational changes. Specifically, residues Yarg254 and ygln255 in the carboxyl terminal

helix form hydrogen bongs with PE-asp317, PE-thr318 and PE-asp319. Also, a second "catch" is

formed between the carboxyl terminal domain of the PT Subunit and the short helix of the

y subunit. Hydrogen bonds formed between Yylss, Yys,90 and Yalnso with PT-asp394 and PT-

glu398. This sequence of the P subunit, DELSEED (P394- 400), iS a portion of the binding

site of amphipathic cationic inhibitors and putatively the ATPase inhibitor protein (81-

83). Recently, mutations of residues involved in the "catch" loops were shown in inhibit

ATP hydrolysis activity by the soluble F1-ATPase (84). Structural information suggests

the two antiparallel coiled coil a-helices of the y subunit may unwind during rotational

catalysis and the a subunit rotates around the Fl axis while undertaking a net translation

of about 23 A+ (85). It is likely that these gross changes observed in the structures

revealed individual functional states of the enzyme complex during catalysis.

The E subunit

 The a subunit ofE. coli F1Fo ATP synthase consists of 138 amino acids with a

molecular weight of 15, 068 Da and is encoded by the uncC gene. The a subunit has

several putative functions in the F1Fo ATP synthase complex including structural,

inhibitory and coupling roles. Structurally, the binding of F1 to Fo has long been known