Isolation and characterization of BetaM protein encoded by ATP1B4 - a unique member of the Na,K-ATPase β-subunit gene family

► Structural properties of BetaM and Na,K-ATPase β-subunits are sharply different. ► BetaM protein is concentrated in nuclear membrane of skeletal myocytes. ► BetaM does not associate with a Na,K-ATPase α-subunit in skeletal muscle. ► Polypeptide chain of the native BetaM is highly sensitive to endogenous proteases. ► BetaM in neonatal muscle is a product of alternative splice mRNA variant B.