The Non-Gastric H+/K+ ATPase (ATP12A) Is Expressed in Mammalian Spermatozoa

H+/K+ ATPase Type 2 is an heteromeric membrane protein involved in cation transmembrane transport and consists of two subunits: a specific alpha subunit (ATP12A) and a non-specific beta subunit. The aim of this study was to demonstrate the presence and establish the localization of ATP12A in spermatozoa from Bubalus bubalis, Bos taurus and Ovis aries. Immunoblotting revealed, in all three species, a major band (100 kDa) corresponding to the expected molecular mass. The ATP12A immunolocalization pattern showed, consistently in the three species, a strong signal at the acrosome. These results, described here for the first time in spermatozoa, are consistent with those observed for the beta(1) subunit of Na+/K+ ATPase, suggesting that the latter may assemble with the alpha subunit to produce a functional ATP12A dimer in sperm cells. The above scenario appeared to be nicely supported by 3D comparative modeling and interaction energy calculations. The expression of ATP12A during different stages of bovine sperm maturation progressively increased, moving from epididymis to deferent ducts. Based on overall results, we hypothesize that ATP12A may play a role in acrosome reactions. Further studies will be required in order to address the functional role of this target protein in sperm physiology.