Isolation and characterization of a mannose-specific endocytosis receptor from human placenta

A receptor which recognizes glycoproteins bearing terminal mannose residues has been isolated from human placental membranes. Washed membranes were solubilized with buffer containing 1% Triton X-100 and applied to a mannose-Sepharose affinity column. The column was eluted with buffer containing 200 mM mannose and 1% cholate. The major protein eluted exhibited a molecular weight of 175 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein binds 125I-labeled mannosylated bovine serum albumin in a saturable fashion with a dissociation constant of 4 nM. Ligand binding is pH-dependent with maximal binding above pH 6.5. This binding can be inhibited with EDTA, mannose, fucose, mannan, beta-glucuronidase, and bovine serum albumin conjugated to fucose. Polyclonal antibodies generated against the mannose binding protein immunoprecipitate a single 175-kDa protein species from both surface-iodinated and biosynthetically labeled human monocyte-derived macrophages.