THE 94-KDA TO 97-KDA MOUSE MACROPHAGE MEMBRANE-PROTEIN THAT RECOGNIZES OXIDIZED LOW-DENSITY-LIPOPROTEIN AND PHOSPHATIDYLSERINE-RICH LIPOSOMES IS IDENTICAL TO MACROSIALIN, THE MOUSE HOMOLOG OF HUMAN CD68

We have previously reported the partial purification of a 94- to 97-kD a plasma membrane protein from mouse peritoneal macrophages that binds oxidatively modified low density lipoprotein (OxLDL) and phosphatidyl serine-rich liposomes, We have now identified that protein as macrosia lin, a previously cloned macrophage-restricted membrane protein in the lysosomal-associated membrane protein family (mouse homologue of huma n CD68). Early in the course of purification of the 94- to 97-kDa prot ein, a new OxLDL-binding band at 190-200 kDa appeared and copurified w ith the 94- to 97-kDa protein, The HPLC pattern of tryptic peptides fr om this higher molecular mass Ligand-binding band closely matched that derived from the 93- to 97-kDa band, Specifically, the same three mac rosialin-derived tryptic peptides (9, 9, and 15 residues) were present in the purified 94- to 97-kDa band and in the 190- to 200-kDa band an d antisera raised against peptide sequences in macrosialin recognized both bands, An antiserum against macrosialin precipitated most of the 94- to 97-kDa OxLDL-binding material, We conclude that the binding of OxLDL to mouse macrophage membranes is in part attributable to macrosi alin, Our previous studies show that OxLDL competes with oxidized red blood cells and with apoptotic thymocytes for binding to mouse periton eal macrophages, Whether macrosialin plays a role in recognition of Ox LDL and oxidatively damaged cells by intact macrophages remains uncert ain.