A MONOCLONAL-ANTIBODY THAT RECOGNIZES A CARBOHYDRATE EPITOPE ON N-LINKED GLYCOPROTEINS RESTRICTED TO A SUBSET OF CHITIN-RICH FUNGI

Previous studies with a monoclonal antibody (designated UB7) raised ag ainst isolated haustorial complexes formed by the pea powdery mildew f ungus Erysiphe pisi showed that it recognized an abundant glycoprotein found in cell walls and plasma membranes of haustoria and the surface mycelium. In this paper, Western blotting and phase-partitioning in t he detergent Triton X-114 have been used to show that the plasma membr ane antigens recognized by UB7 comprise a 62 kDa integral glycoprotein and a set of integral membrane glycoproteins of lower molecular weigh t. A 59 kDa glycoprotein recognized by UB7 has been extracted from the fungus using aqueous buffer, and the evidence suggests that this repr esents the cell wall form of the antigen. Binding of UB7 is abolished by pre-treatment of glycoproteins with peptide-N-glycosidase, but is r etained after endo-F treatment. This suggests that the epitope to whic h UB7 binds is the innermost N-acetylglucosamine residue of N-linked c arbohydrate side chains of glycoproteins, possibly substituted with on e or more sugars. When tested for cross-reactivity with other fungi, U B7 bound to some, but not all, of those examined, and recognized diffe rent sets of glycoproteins compared with those detected in E. pisi. Ho wever, UB7 did not bind to any higher plants nor to any animal glycopr oteins tested. This antibody thus identifies a carbohydrate epitope re stricted to glycoproteins in a subset of the fungi.