FIG. 1.

Sequence alignment of the atpE gene products from selected species. The sequences form an α-helical hairpin. A cytoplasmic loop (shown in black) connects both helices. The H⁺- or Na⁺-binding glutamate on the C-terminal helix is shown in red. The residues involved in Na⁺ binding and the hydrogen bridge-providing tyrosine are shown in yellow. At the end of the alignment, the corresponding coupling ion (C) of the corresponding ATP synthase is indicated. The amino acids which are in the area of the 2D crystal contacts are shown in dark green (cytoplasmic side) and blue (periplasmic side). The numbering of the amino acids is according to that of the C. paradoxum sequence (7). The selected species are Clostridium paradoxum (CP), Ilyobacter tartaricus (IT), Acetobacterium woodii c2/3 (AW), Bacillus strain PS3 (PS3), Spinacia oleracea (SO), and Escherichia coli (EC.