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NKAα4 undergoes phosphorylation in sperm during capacitation
Jack, Jarrid
Jack, Jarrid
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Abstract
Na, K-ATPase (NKA) is a plasma membrane protein responsible for establishing the typical Na+ and K+ electrochemical gradients that most cells maintain between their environment and the cytosol. In mammals, NKA is expressed as different isoforms of both the catalytic α (NKAα1, NKAα2, NKAα3 and NKAα4) and glycosylated β (NKAβ1, NKAβ2 and NKAβ3) subunits that form the transporter. These isoforms have a particular expression that is tissue dependent and possess different functional properties. Among them, NKAα4 has the most restricted pattern of expression, being limited to male germ cells of the testis and mature sperm. NKAα4 is essential for sperm and its deletion in mice results in complete male infertility. By directly controlling intracellular Na+ and K+ levels and secondarily H+ and Ca2+, NKAα4 has a key role in sperm motility. Previous studies in our laboratory have shown that NKAα4 activity is regulated during sperm capacitation, an event that is required for sperm fertility. However, at present, the mechanisms involved in this upregulation of function are unknow. Phosphorylation is one of the primary mechanisms that sperm use to regulate protein function; therefore, we here studied if NKAα4 is the target of sperm capacitation dependent phosphorylation. Using immunoprecipitation of NKAα4 followed by immunoblot determination of phosphorylated residues, we show that NKAα4 is phosphorylated and that this increases during sperm capacitation. Mass spectrometry of immunoprecipitated NKAα4 identified a serine residue (Ser461 in rat and 463 in mouse) which is the target of phosphate addition. Interestingly, this serine is shared in humans. The high conservation of this phosphorylation site points to the importance that phosphorylation may have in the regulation of NKAα4.
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2025-01-01
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University of Kansas
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Physiology