CBP70, A GLYCOSYLATED NUCLEAR LECTIN

Some years ago, a lectin designated CBP70 that recognized glucose (Glc ) but had a stronger affinity for N-acetylglucosamine (GlcNAc), was fi rst isolated from HL60 cell nuclei. Recently, a cytoplasmic form of th is lectin was described, and one 82 kDa nuclear ligand was characteriz ed for the nuclear CBP70. In the present study, the use of Pronase dig estion and the trifluoromethanesulphonic acid (TFMS) procedure strongl y suggest that the nuclear and the cytoplasmic CBP70 have a same 23 kD a polypeptide backbone and, consequently, could be the same protein. I n order to know the protein better and to obtain the best recombinant possible in the future, the post-translational modification of the nuc lear and cytoplasmic CBP70 was analyzed in terms of glycosylation; Sev erals lines of evidence indicate that both forms of CBP70 are N- and O -glycosylated. Surprisingly, this glycosylation pattern differs betwee n the two forms, as revealed by beta-elimination, hydrazinolysis, pept ide-N-glycosydase F (PNGase F), and TFMS reactions. The two preparatio ns were analyzed by affinity chromatography on immobilized lectins [Ri cinus communis-l agglutinin (RCA-I), Arachis hypogaea agglutinin (PNA) , Galanthus nivalis agglutinin (GNA), and wheat germ agglutinin (WGA)] and by lectin-blotting analysis [Sambucus nigra agglutinin (SNA), Maa ckia amurensis agglutinin (MAA), Lotus tetragonolobus (Lotus), succiny lated-WGA, and Psathyrella velutina agglutinin (PVA)]. Both forms of C BP70 have the following sugar moities: terminal beta Gal residues, Gal beta 1-3 GalNAc, Man alpha 1-3 Man, sialic acid alpha 2-6 linked to G al or GalNAc; and sialic acid alpha 2-3 linked to Gal. However, only n uclear CBP70 have terminal GlcNAc and alpha-L-fucose residues. All the se data are consistent with the fact that different glycosylation patt ern found for each form of CBP70 might act as a complementary signal f or cellular targeting. (C) 1997 Wiley-Liss, Inc.