CHAPTER 5
MUTAGENISIS OF THE AMINO AND CARBOXYL TERMINI OF THE b SUBUNIT
 IN F1Fo ATP SYNTHASE

 Introduction

 Two stalk structures have been shown to link the Fl and Fo sectors (11, 187). The

central, or "rotary" stalk, extends within the u3 3 hexamer. Protons diffuse through the

membrane, via the a and c subunits of Fo, resulting in the rotation of the central stalk

within the hexamer, ultimately generating ATP (4, 16, 189). The peripheral stalk, or

"stator", is positioned to the side of the F1Fo ATP synthase complex and reaches from the

periplasmic leaflet of the membrane up to near the top of Fl, in an a-helical highly

extended conformation (12, 13, 166, 204, 294), where it makes contact with a single a

subunit (100, 141-143). The primary function of the peripheral stalk is to prevent the

rotation of the u3 3 hexamer against the rotation of the central stalk.

 The peripheral stalk consists of the 6 subunit of Fl and the b subunit dimer of Fo

(198, 288), which have been shown to be in direct contact with each other at their

carboxyl termini (3, 4, 200, 219, 220). The b subunit dimer is the major component of

the peripheral stalk, anchoring Fl to the membrane. Despite attempts by several other

laboratories, there is presently no high-resolution structure of the entire b subunit.

Therefore, model polypeptides have been constructed in order to elucidate the structure

of the b subunit by domain. Four domains comprise the b subunits: the amino terminal

membrane-spanning, tether, dimerization and the carboxyl terminal 6-binding domains

(Figure 5-1) (12, 13). A model polypeptide comparable to residues 1-34, which contains