Abstract
H+/K+ ATPase Type 2 is an heteromeric membrane protein involved in cation transmembrane transport and consists of two subunits: a specific α subunit (ATP12A) and a non-specific β 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 β1 subunit of Na+/K+ ATPase, suggesting that the latter may assemble with the α 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.
Highlights
IntroductionIt consists of an α and a β subunit [1,2] for which their assembly is required for their functional expressions
The “non gastric” H+/K+ ATPase is a transmembrane heterodimer responsible for H+efflux in exchange with K+
Together with the “gastric” H+/K+ ATPase and Na+/K+ ATPase, the “non gastric” H+/K+ ATPase forms the subgroup of the so-called X-K-ATPases, which is member of the P2C-type ATPases, a large family of integral membrane transporters responsible for generating and maintaining essential electro-chemical gradients across cellular membranes by pumping ions using the energy from ATP hydrolysis [10,11]
Summary
It consists of an α and a β subunit [1,2] for which their assembly is required for their functional expressions. The α subunit specific for the “non gastric” H+/K+ ATPase is known as ATP12A. From studies carried out in various cell types, the β subunit of the “gastric” H+/K+ ATPase (i.e., ATP4B) and one of the β subunits of the Na+/K+ ATPase, known as ATP1B1, ATP1B2 and ATP1B3, have been proposed as possible candidates for interaction with ATP12A [1,4,5,6,7,8,9]. X-K-ATPases transporters are conserved across many species, and they can be observed ubiquitously in all cell types (as in the case of Na+/K+ ATPase) or with a less broad patterns of expression.
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