Previous studies with a monoclonal antibody (designated UB7)
raised against isolated haustorial complexes formed by the pea
powdery mildew fungus 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 the detergent Triton X-114
have been used to show that the plasma membrane antigens recognized
by UB7 comprise a 62 kDa integral glycoprotein and a set of integral
membrane glycoproteins of lower molecular weight. A 59 kDa
glycoprotein recognized by UB7 has been extracted from the fungus
using aqueous buffer, and the evidence suggests that this represents
the cell wall form of the antigen. Binding of UB7 is abolished by
pre-treatment of glycoproteins with peptide-N-glycosidase,
but is retained after endo-F treatment. This suggests that the
epitope to which UB7 binds is the innermost
N-acetylglucosamine residue of N-linked
carbohydrate side chains of glycoproteins, possibly substituted with
one or more sugars. When tested for cross-reactivity with other
fungi, UB7 bound to some, but not all, of those examined, and
recognized different sets of glycoproteins compared with those
detected in E. pisi. However, UB7 did not bind to any higher
plants nor to any animal glycoproteins tested. This antibody thus
identifies a carbohydrate epitope restricted to glycoproteins in a
subset of the fungi.