The Light Chain of CD98 Is Identified as E16/TA1 Protein

Abstract

The 80/40-kDa CD98 protein complex was purified using an anti-CD98 heavy chain monoclonal antibody coupled to Sepharose beads. Eluted proteins were subjected to preparative SDS-polyacrylamide gel electrophoresis, and protein corresponding to the 40-kDa CD98 light chain was excised. Following proteolysis with trypsin, a peptide fragment was sequenced by mass spectrometry. The nine residues obtained were identical to established C-terminal sequences of the human E16 and rat TA1 proteins, suggesting that TA1/E16 protein is the CD98 light chain. Consistent with this, anti-TA1/E16 antibodies specifically immunoblotted the approximately 35-40-kDa light chain present upon immunoprecipitation of the human CD98 complex. Furthermore, anti-CD98 heavy chain antibody specifically co-immunoprecipitated hemagglutinin-tagged light chain from cells transfected with hemagglutinin-tagged E16 cDNA. In conclusion, the CD98 light chain is identical to the TA1/E16 protein, based on partial amino acid sequence identity, antibody cross-reactivity, genetic reconstitution evidence, similar molecular size, and comparable cell distribution.