A major concanavalin-A-binding cell surface protein from normal and leukemic granulocytes: isolation and characterization.

This paper reports the isolation and biochemical characterization of a major concanavalin A (Con A)-binding cell surface protein (protein 2, M(r) 75-85 kD) from normal and chronic myeloid leukemic (CML) granulocytes. Our studies show that protein 2 has two differentially glycosylated forms, protein 2a (M(r) 75-85 kD), which does not bind the lectin RCA, and protein 2b (M(r) 80-90 kD), which does. Both molecules show identical retention times on reverse-phase HPLC, irrespective of the cell source. By the procedure used the amount of 2a obtained is about 2.4 times more than that of 2b in normal cells and about 2.6 times more in CML cells. Furthermore, both are approximately 2.4-fold more in CML granulocytes. A polyclonal antibody to protein 2a also immunostains protein 2b. The antibody to protein 2a does not prevent Con A binding but inhibits its internalization. Similarity of the molecules from both the cell types and their increased amounts in CML granulocytes suggest that factors/components other than its structure and amount are responsible for the known defective internalization of Con A by CML granulocytes.