Three complement-type repeats of the low-density lipoprotein receptor-related protein define a common binding site for RAP, PAI-1, and lactoferrin.
The low-density lipoprotein receptor-related protein (LRP) is a 600-kD scavenger receptor that binds a number of protein ligands with high affinity. Although some ligands do not compete with each other, binding of all is uniformly blocked by the 39-kD receptor-associated protein (RAP). RAP is normally found in the endoplasmic reticulum and seems to function as a chaperone for LRP. To identify the binding sites for RAP, lactoferrin, and plasminogen activator inhibitor-1 (PAI-1), a bacterial expression system has been developed to produce soluble LRP fragments spanning residues 783-1399. These residues overlap most of the CNBr fragment containing the second cluster of complement-type repeats (C). Solid phase binding assays show that 125I-RAP binds to fragments containing three successive complement-type repeats: C5-C7. PAI-1 and lactoferrin bind to the same fragments. A fragment containing C5-C7 also blocks uptake and degradation of 125I-RAP by fibroblasts in a concentration-dependent manner. Binding competition experiments show that RAP, PAI-1, and lactoferrin each inhibit the binding of the others, suggesting that at this site in LRP, RAP acts as a competitive, rather than an allosteric, inhibitor of PAI-1 and lactoferrin binding.
Vash
B
B
Departmnt of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Phung
N
N
Zein
S
S
DeCamp
D
D
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D003165:Complement System Proteins / Q000737:chemistry*; D005347:Fibroblasts / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D026563:LDL-Receptor Related Protein-Associated Protein; D007781:Lactoferrin / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008565:Membrane Proteins; D051379:Mice; D010446:Peptide Fragments / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism*; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000737:chemistry / Q000378:metabolism*; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D051122:Scavenger Receptors, Class B
D002352:Carrier Proteins; D006023:Glycoproteins; D026563:LDL-Receptor Related Protein-Associated Protein; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008565:Membrane Proteins; D010446:Peptide Fragments; D017395:Plasminogen Activator Inhibitor 1; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011993:Recombinant Fusion Proteins; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D003165:Complement System Proteins; D007781:Lactoferrin