Mechanism of proton pumping by plant plasma membrane H+-ATPase: role of residues in transmembrane segments 5 and 6.

The mechanism of proton pumping by P-type plasma membrane H(+)-ATPases is not well clarified. Site-directed mutagenesis studies suggest that Asp684, situated in transmembrane segment M6, is involved in coordination of proton(s) in plant plasma membrane H(+)-ATPase. This hypothesis is supported by atomic models of H(+)-ATPases built on the basis of the crystal structure of the related SERCA1a Ca(2+)-ATPase. However, more biochemical, genetic, and structural studies are required before we will be able to understand the nature of the proton binding site(s) in P-type H(+)-ATPases and the mechanism of action of these pumps.