Expression of (Na, K) ATPase/Ca-ATPase chimeric proteins in Xenopus oocytes revealed that the COOH-terminal one-third of the (Na, K) ATPase alpha-subunit is involved in assembly with the beta-subunit.

Abstract

Chimeric proteins consisting of parts from the alpha-subunit of Torpedo californica (Na, K) ATPase (N) and the rabbit sarcoplasmic reticulum Ca-ATPase (C) were expressed in Xenopus oocytes by injecting the respective chimeric cRNA in combination with cRNA for the beta-subunit of Torpedo (Na, K) ATPase. The chimeric protein (NCN) that consisted of the NH2-terminal and COOH-terminal one-thirds of the alpha-subunit of the (Na, K) ATPase and the central one-third of the Ca-ATPase was able to assemble with the beta-subunit in the same fashion as the wild-type alpha-subunit of the (Na, K) ATPase (NNN). On the other hand, chimeric proteins in which the COOH-terminal one-third was derived from the Ca-ATPase (NNC and NCC) were unable to form stable complexes with the beta-subunit. These results suggest that the COOH-terminal one-third of the (Na, K) ATPase alpha-subunit is required for the assembly with the beta-subunit.