Figure 2.

Diagram showing best BLAST hit relationships between ATP synthases, subunit A (Figure 2A) and subunit B (Figure 2B) for two bacteria, Escherichia coli and Bacillus subtilis, and two archaea, Methanosarcina mazei and Sulfolobus solfataricus. Some confusion prevails in the annotation of ATP synthase subunits for bacteria and archaea: the beta chain in bacteria is the catalytic subunit and corresponds to subunit A in archaeal and eukaryotic vacuolar type ATPases; the alpha chain, or non-catalytic subunit, in bacteria corresponds to subunit B in archaea [46]. In addition, the archaeal A subunit is sometimes labelled as alpha subunit. To simplify our discussion and the diagrammatic representation we designate all catalytic subunits, either from bacteria or from archaea as ATP-A, and all non-catalytic subunits as ATP-B.