Anticipating antiport in P-type ATPases.

Cation-transporting P-type ATPases show a high degree of structural and functional homology. Nevertheless, for many members of this large family, the molecular mechanism of transport is unclear; namely, whether transport is electrogenic or not and if countertransport is involved remains to be established. In a few well-studied cases such as the Na(+)-K(+)-ATPase, plasma membrane Ca(2+) ATPase (PMCA) and sarcoplasmic reticulum Ca(2+) ATPase (SERCA) countertransport has been clearly demonstrated. New data based on the crystal structure of SERCA now strongly indicate that countertransport could be mandatory for all P-type ATPases. This concept should be verified for other known and for all newly characterized P-type ATPases.