Functional Consequences of Substitution of the Disulfide-Bonded Segment, Cys127-Cysl50, Located in the Extracellular Domain of the Na,K-ATPase β Subunit: Argl48 Is Essential for the Functional Expression of Na,K-ATPase

• Published in: Journal of biochemistry (Tokyo) 1995-03, Vol.117 (3), p.591-596
• Main Authors: Ueno, Susumu, Kusaba, Miyuki, Takeda, Kazuo, Maeda, Masatomo, Futai, Masamitsu, Izumi, Futoshi, Kawamura, Masaru
• Format: Article
• Language: English
• Subjects: disulfide bond; K-ATPase; Xenopus oocyte; β subunit
• ISSN: 0021-924X
• DOI: 10.1093/oxfordjournals.jbchem.a124749

The Cys127-Cys150 disulfide-bonded loop (L,) of the Torpedo californica Na,K-ATPase β1 subunit was substituted with the corresponding loop of the rat β1, mouse β2, or pig H,K-ATPase β subunit. All the substituted mutant β subunits assembled with the Na,K-ATPase α subunit in a trypsin-resistant manner. The mutants with L, from the Na,K-ATPase β subunit isoforms (rat β1 and mouse β2) each formed a functional complex with the Na,K-ATPase α subunit. On the other hand, the complex of the α subunit with the mutant β subunit that was substituted with the pig H,K-ATPase β subunit L1 was inactive as to ATP hydrolysis. Ser131 and Phe148 located within L1 of the pig H,K-ATPase β subunit-substituted mutant were back-mutated to Pro131 and Arg148, respectively. The Phe148 to Arg mutation restored the ability of the mutant β subunit substituted with the H,K-ATPase β subunit L1 to form a functional complex with the α subunit. These results suggested that the Cys127–Cys150 loop of the Na,K-ATPase β1 subunit, especially Arg148, plays a critical role in the functional expression of Na,K-ATPase.