74=, 75= 78 227= 228 a,
 t 200 bend a a
 ++ A* A* A f 40
 MNLNATILGQ AIAFVLFVLF CMKYVWVPPLM AAlEKRQKEl
 Mnembrane-Spanning Tether



 At* .. X 8
 ADGLASAERA HKDLDLAKAS AT











 QVAILAVA GAEKllERSV DEAANSDIVD KLVAEL

 F,-Binding






Figure 1-5. Amino acid sequence of the E. coli F1Fo ATP synthase b subunit. The E. coli
 b subunit is a 156 residue amphipathic polypeptide. The amino acid sequence
 and the four domains are shown. The transmembrane domain (bl-22), tether
 domain (b24-60), dimerization domain (b63-122) and the 6-binding domain (bl23-
 156) are Shown in blue, orange, green and red, respectively. The large purple
 stars indicate residues capable of forming high yields of b-b crosslinks upon
 cysteine substitution. The smaller purple stars indicate residues found to form
 low-yields of crosslinks. The arrows indicate positions crosslinked to other
 subunits of ATP synthase. High-resolution structures based on model
 polypeptides consisting of bl-34 and b62-122 (underlined residues) have been
 solved by NMR and crystallography, respectively. NMR analysis of residues
 1-34 has revealed a a-helical structure with a rigid 200 bend at positions 23-
 26. X-ray crystallography revealed a highly a-helical structure with modeled
 into a right-handed coiled coil.