A small number of taxonomically diverse prokaryotic species have what appears to be a second ATP synthase, in addition to the normal F1F0 ATPase in bacteria and A1A0 ATPase in archaea. These enzymes use ion gradients to synthesize ATP, and in principle may run in either direction. This model represents the F1 beta subunit of this apparent second ATP synthase.
Jiyao W et al.(2023). "The conserved domain database in 2023.",