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Role of N‐glycans of the β 2 subunit in assembly and trafficking of the α 1 β 2 Na,K‐ATPase
Author(s) -
Vagin Olga,
Tokhtaeva Elmira,
Sachs George
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.875.4
Subject(s) - calnexin , protein subunit , chaperone (clinical) , glycosylation , golgi apparatus , endoplasmic reticulum , chemistry , biology , biochemistry , calreticulin , gene , medicine , pathology
The non‐glycosylated αsubunit of the Na,K‐ATPase is unable to exit the ER unless it is co‐expressed with the N‐glycosylated ? subunit. We tested whether N‐glycans of the ? 2 subunit are required for proper folding, assembly and quality control of the Na,K‐ATPase in the ER. The over‐expressed ? 2 subunit was co‐localized with the endogenous α 1 and ? 1 subunits in the plasma membrane of MDCK cells and co‐immunoprecipitated with the α 1 subunit from cell lysates. A minor fraction of the ? 2 subunit was detected in the ER without the α 1 subunit. The ? 2 subunit, but not the α 1 subunit, was co‐immunoprecipitated with the ER chaperone, calnexin. Mutation of more than three of the eight N‐glycosylation sites of the ? 2 subunit prevented α 1 ? 2 assembly, augmented association of the ? 2 subunit with calnexin, and resulted in complete retention of the ? 2 subunit in the ER. In contrast, the endogenous α 1 subunit was neither associated with calnexin nor retained in the ER. Thus, particular N‐glycans are required for calnexin‐mediated folding and quality control of the unassembled ? 2 subunit, but not of the α 1 ? 2 complex. The proper folding of the ? 2 subunit is a prerequisite for the α 1 ? 2 assembly, which, in turn, is necessary for the export of the ? 2 subunit from the ER to the Golgi. Therefore, neither the α 1 nor the β 2 subunits are able to exit the ER unless they are assembled in the full enzyme. Supported by NIH, DK077149 and DK58333.