Characterization of residues and sequences of the carbohydrate recognitiondomain required for cell surface localization and ligand binding of human lectin-like oxidized LDL receptor

Lectin-like oxidized low-density lipoprotein receptor (LOX-I) has been clon ed from human aortic endothelial cells, and has a sequence identical to tha t from human lung. Previous studies showed that human LOX-1 can recognize m odified LDL, apoptotic cells and bacteria. To further explore the relations hip between the structure and function of LOX-1, a mutagenesis study was ca rried out. Our results showed that the carbohydrate recognition domain (CRD ) was the ligand-binding domain of human LOX-1. We also investigated the se quences and residues in CRD that were essential for protein cell surface lo calization and ligand binding, LOS-ls carrying a mutation on each of sir Cy s in CBD resulted in a variety of N-glycosylation and failed to be transpor ted to the cell surface, This was strong evidence for the involvement of al l six Cys in the intrachain disulfide bonds required for proper folding, pr ocessing and transport of LOX-I. The C-terminal sequence (KANLRAQ) was also essential for protein folding and transport, while the four final residues (LRAQ) were involved in maintaining receptor function. Both positive charg ed (R208, R209, H226, R229 and R231) and non-charged hydrophilic (Q193, S19 8, S193 and N210) residues were involved in ligand binding, suggesting that ligand recognition of LOX-1 is not merely dependent on the interaction of positively charged residues with negatively charged ligands.