β subunit affects Na⁺ and K⁺ affinities of Na⁺/K⁺-ATPase: Na⁺ and K⁺ affinities of a hybrid Na⁺/K⁺-ATPase composed of insect α and mammalian β subunits.

ABSTRACT: The affinity for K⁺ of silkworm Na⁺/K⁺-ATPase, which is composed of α and β subunits, is remarkably lower than that of mammalian Na⁺/K⁺-ATPase, with a slightly higher affinity for Na⁺. Because the α subunit had more than 70% identity to the mammalian α subunit in the amino acid sequence, whereas the β subunit, a glycosylated protein, had less than 30% identity to the mammalian β subunit, it was suggested that the β subunit was involved in the affinities for Na⁺ and K⁺ of Na⁺/K⁺-ATPase. To confirm this hypothesis, we examined whether replacing the silkworm β subunit with the mammalian β subunit affected the affinities for Na⁺ and K⁺ of Na⁺/K⁺-ATPase. Cloned silkworm α and cloned rat β1 were co-expressed in BM-N cells, a cultured silkworm ovary-derived cell lacking endogenous Na⁺/K⁺-ATPase, to construct a hybrid Na⁺/K⁺-ATPase, in which the silkworm β subunit was replaced with the rat β1 subunit. The hybrid Na⁺/K⁺-ATPase increased the affinity for K⁺ by 4.1-fold and for Na⁺ by 0.65-fold compared to the wild-type one. Deglycosylation of the silkworm β subunit did not affect the K⁺ affinity. These results support the involvement of the β subunit in the Na⁺ and K⁺ affinities of Na⁺/K⁺-ATPase.

SUBMITTER: Homareda H 

PROVIDER: S-EPMC9483571 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature