Isolation of the SO4-4-GalNAc beta 1,4GlcNAc beta 1,2Man alpha-specific receptor from rat liver

Glycoproteins, such as the glycoprotein hormone lutropin (LH), bear oligosaccharides terminating with the sequence SO4-4GalNAc beta 1,4GlcNAc beta 1,2Man alpha (S4GGnM) and are rapidly removed from the circulation by a receptor present in hepatic endothelial cells and Kupffer cells, Rapid removal from the circulation is essential for attaining maximal hormone activity in vivo. We have isolated a protein from rat liver which has the properties expected for the S4GGnM-specific receptor (S4GGnM-R). The S4GGnM-R is closely related to the macrophage mannose receptor (Man-R) both antigenically and structurally. At least 12 peptides prepared from the S4GGnM-R have amino acid sequences that are identical to those of the Man-R, Nonetheless, the ligand binding properties of the S4GGnM-R and the Man-R differ in a number of respects, The S4GGnM-R binds to immobilized LH but not to immobilized mannose, whereas the Man-R binds to immobilized mannose but not to immobilized LH, When analyzed using a binding assay that precipitates receptor ligand complexes with polyethylene glycol, the S4GGnM-R is able to bind S4GGnM-bovine serum albumin (S4GGnM-BSA) conjugates gates whereas the Man-R is not, In contrast both the S4GGnM-R and the Man-R are able to bind Man-BSA. Monosaccharides that inhibit binding of Man-BSA by the Man-R enhance binding by the S4GGnM-R. Oligosaccharides terminating with S4GGnM and those terminating with Man are bound at independent sites on the S4GGnM-R, The S4GGnM-R present in hepatic endothelial cells may account for clearance of glycoproteins bearing oligosaccharides terminating with S4GGnM and glycoproteins bearing oligosaccharides terminating with either mannose, fucose, or N-acetylglucosamine.