LIGAND RECOGNITION BY PURIFIED HUMAN MANNOSE RECEPTOR

In this work we examine the carbohydrate binding properties of human placental mannose receptor (HMR) using a rapid and sensitive enzyme-linked immunosorbent microplate assay. The assay is based on the inhibition of binding of highly purified receptor to yeast mannan-coated 96-well plates. The specificity of ligand binding was inferred from the potency of different saccharides in blocking HMR binding to the mannan-coated wells. The relative inhibitory potency of monosaccharides was l-Fuc > d-Man > d-Glc > d-GlcNAc > Man-6-P ≫ d-Gal ≫ l-Rha ≫ GalNAc. The inhibitory potency of mannose increased by two orders of magnitude when linear oligomers were used. Oligomers containing α-1-3- and α-1-6-linked mannose residues were more inhibitory than those containing α-1-2- and α-1-4-linked mannoses. Linear or branched oligomannosides larger than three units did not have a significant influence on their inhibitory potency; rather, potency was found to decrease in comparison with oligomannosides with three units. Compared to linear oligomers, inhibition of binding was the best using branched mannose oligosaccharides, α-d-Man-bovine serum albumin conjugates, or mannan. A model is discussed in which branched ligand is bound to spatially distinct sites on the HMR. © 1992.