STRUCTURAL STUDY OF THE SUGAR CHAINS OF CD36 PURIFIED FROM BOVINE MAMMARY EPITHELIAL-CELLS - OCCURRENCE OF NOVEL HYBRID-TYPE SUGAR CHAINS CONTAINING THE NEU5AC-ALPHA-2-]6GALNAC-BETA-1-]4GLCNAC AND THE MAN-ALPHA-1-]2MAN-ALPHA-1-]3MAN-ALPHA-1-]6MAN GROUPS

CD36 is a glycoprotein included in the bovine milk fat globule membran e derived from mammary secretory epithelial cells during lactation. As paragine-linked sugar chains were quantitatively released from CD36 as oligosaccharides by hydrazinolysis. These sugar chains were converted to radioactive oligosaccharides by reduction with (NaBH4)-H-3 and sep arated into neutral and acidic fractions by paper electrophoresis. Mos t of the acidic oligosaccharides were converted to neutral ones by sia lidase digestion, indicating that they are sialyl derivatives. The neu tral and sialidase-treated acidic oligosaccharides were fractionated b y Bio-Gel P-4 column chromatography in combination with serial chromat ography on immobilized lectin columns including a Wistaria floribunda agglutinin (WFA)-agarose column. WFA is known to bind oligosaccharides terminating with either an alpha- or beta-N-acetylgalactosamine resid ue. Structural studies of oligosaccharides in each fraction by sequent ial exoglycosidase digestion as well as methylation analysis revealed that CD36 contains high mannose-type, hybrid-type, and bi-, tri-, and tetraantennary complex-type sugar chains. A portion of the hybrid-type and the complex-type sugar chains which bound to a WFA-agarose column (28% of all oligosaccharides) contained the GalNAcbeta1-->4GlcNAc gro up(s) instead of the Galbeta1-->4GlcNAc group(s) in their outer chain moieties. Like oligosaccharides found in human luteinizing hormone [We isshaar, G., Hiyama, J., Renwick, A. G., & Nimtz, M. (1991) Eur. J. Bi ochem. 195, 257-268], some of the GalNAcbeta1-->4GlcNAc groups found i n the CD36 oligosaccharides were sialylated as the Neu5Acalpha2-->6Gal NAc group. Furthermore, most of the hybrid-type sugar chains of CD36 w ith the Gal/GalNAcbeta1-->4GlcNAcbeta1-->2 outer chain on their Manalp ha1-->3 arm contained an unusual Manalpha1-->2Manalpha1-->3 group on t heir Manalpha1-->6 arm.