Recombinant Human LRP-1 Cluster II Fc Chimera Protein, CF

LDL receptor-related protein 1 (LRP-1), also known as CD91 and the alpha2-macroglobulin receptor, is a type I transmembrane protein in the LDL receptor superfamily. It is expressed on neurons, hepatocytes, adipocytes, vascular smooth muscle cells, fibroblasts, keratinocytes, macrophages, and megakaryocytes. LRP-1 is important for the clearance of a large number of circulating molecules involved in fatty acid metabolism and the inhibition of serine proteases (1 - 4). LRP-1 also associates, or through intracellular scaffold proteins, with other membrane associated proteins on the same cell. This allows LRP-1 to modulate the activity or internalization of PDGF R beta, NMDA receptor subunits, TGF-beta receptors, Frizzled-1, various integrins, and the prion protein PrP^C (1, 5 - 10). Human LRP 1 is N glycosylated and sialylated, and cleaved in the Golgi to produce an 85 kDa transmembrane beta chain, and a 515 kDa alpha chain. Both associate noncovalently, with the beta chain remaining completely extracellular (11, 12). The alpha chain of LRP 1 contains 31 LDLR class A repeats, 34 LDLR class B repeats, and 22 EGF-like repeats (13). The LDLR domains are clustered in four regions throughout the protein (13). Cluster II (aa 786 - 1165) contains one EGF-like and eight LDLR class A repeats (14, 15). Cluster II contains binding sites for Apolipoprotein E, LPL, LRPAP/RAP, alpha 2 Macroglobulin, Coagulation Factor VIII light chain, Lactoferrin, PAI-1, tPA-PAI-1 complexes, Pro-uPA, and TFPI (14, 15). Within this region, human LRP-1 shares 99% aa sequence identity with mouse and rat LRP-1. A shed soluble form of LRP-1 circulates in the serum and retains ligand binding properties (16).