F-0 complex of the Escherichia coli ATP synthase - Not all monomers of thesubunit c oligomer are involved in F-1 interaction

The antigenic determinants of mAbs against subunit c of the Escherichia col i ATP synthase were mapped by ELISA using overlapping synthetic heptapeptid es. All epitopes recognized are located in the hydrophilic loop region and are as follows: 31-LGGKFLE-37, 35-FLEGAAR-41, 36-LEGAAR-41 and 36-LEGAARQ-4 2. Binding studies with membrane vesicles of different orientation revealed that all mAbs bind to everted membrane vesicles independent of the presenc e or absence of the F-1 part. Although the hydrophilic region of subunit c and particularly the highly conserved residues A40, R41, Q42 and P43 are kn own to interact with subunits gamma and epsilon of the F-1 part, the mAb mo lecules have no effect on the function of F-0. Furthermore, it could be dem onstrated that the F-1 part and the mAb molecule(s) are bound simultaneousl y to the F-0 complex suggesting that not all c subunits are involved in F-1 interaction. From the results obtained, it can be concluded that this inte raction is fixed, which means that subunits gamma and epsilon do not switch between the c subunits during catalysis and furthermore, a complete rotati on of the subunit c oligomer modified with mAb(s) along the stator of the F 1F0 complex, proposed to be composed of at least subunits b and delta, seem s to be unlikely.