IDENTIFICATION OF THE CD45-ASSOCIATED 116-KDA AND 80-KDA PROTEINS AS THE ALPHA-SUBUNITS AND BETA-SUBUNITS OF ALPHA-GLUCOSIDASE-II

CD45 is an abundant, highly glycosylated transmembrane protein-tyrosin e phosphatase expressed on hematopoietic cells. Herein we demonstrate that two proteins of 116 kDa and 80 kDa copurify with CD45 from mouse T cells. Microsequence analysis of the 116-kDa protein revealed high s imilarity to an incomplete human open reading frame that has been sugg ested to correspond to the catalytic alpha-subunit of glucosidase II. We determined the nucleotide sequence of the mouse cDNA and observed t hat it encodes a protein product nearly identical to its human homolog ue and shares an active site consensus sequence with Family 31 glucosi dases. Amino acid sequencing of the 80-kDa protein, followed by molecu lar cloning, revealed high homology to human and bovine cDNAs postulat ed to encode the beta-subunit of glucosidase II. Antisera developed to the mouse beta-subunit allowed us to demonstrate that the interaction between CD45 and glucosidase II can be reconstituted in vitro in an e ndoglycosidase H-sensitive manner. The strong interaction between gluc osidase II and CD45 may provide a paradigm for investigating novel asp ects of the biology of these proteins.