Oligomerization is required for the activity of recombinant soluble LOX-1

LOX-1 is a scavenger receptor that functions as the primary receptor for oxidized low-density lipoprotein (OxLDL) in endothelial cells. The binding of OxLDL to LOX-1 is believed to lead to endothelial activation, dysfunction, and injury, which constitute early atherogenic events. Because of its potential pathological role in atherosclerosis, LOX-1 has been proposed as a therapeutic target for the treatment of this disease. In order to antagonize the ligand-binding function of cell surface LOX-1, we generated a series of recombinant human LOX-1-crystallizable fragment (Fc) fusion proteins and subsequently characterized their biochemical properties and ligand-binding activities in vitro. Consistent with the notion that oligomerization of cell surface LOX-1 is required for high-avidity binding of ligands, we found that LOX-1-Fc fusion protein containing four ligand-binding domains per Fc dimer, but not the one containing two ligand-binding domains, exhibited ligand-binding activity. Optimal ligand-binding activity could be achieved via crosslinking of LOX-1-Fc fusion proteins with a polyclonal antibody against Fc. The crosslinked LOX-1-Fc protein also effectively inhibited the binding and internalization of OxLDL by cell surface LOX-1. These findings demonstrate that functional oligomerization is required for recombinant LOX-1-Fc to function as an effective antagonist.