ASSEMBLY OF THE EXTRACELLULAR DOMAIN OF THE NA,K-ATPASE BETA-SUBUNIT WITH THE ALPHA-SUBUNIT - ANALYSIS OF BETA-SUBUNIT CHIMERAS AND CARBOXYL-TERMINAL DELETIONS

The role of the extracellular domain of the Na,K-ATPase beta subunit i n assembly with the alpha subunit was investigated. A chimeric protein consisting of the extracellular domain of the beta subunit fused with the transmembrane and cytoplasmic domains of dipeptidyl peptidase IV assembles with the alpha subunit. An inverse chimera consisting of the cytoplasmic and transmembrane domains of the beta subunit fused with the extracellular domain of dipeptidyl peptidase IV does not assemble with the alpha subunit. The assembly data from these chimeras demonstr ate that the extracellular domain of the beta subunit is both necessar y and sufficient for assembly with the alpha subunit. Deletions of up to 146 extracellular amino acids from the carboxyl terminus of the bet a subunit appear to result in misfolding of the subunit, but do allow reduced assembly with the alpha subunit. Together, the assembly data f rom chimeras and carboxyl-terminal deletions have identified a 96-resi due extracellular domain which contains sequences involved in subunit assembly. While the chimeric subunits properly localize to the plasma membrane, deletion of as few as 4 amino acids from the carboxyl termin us impairs the ability of the beta subunit to be transported to the pl asma membrane.