Analysis of ligand binding to the alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein. Evidence that lipoprotein lipase and the carboxyl-terminal domain of the receptor-associated protein bind to the same site. 1995

M S Nielsen, and A Nykjaer, and I Warshawsky, and A L Schwartz, and J Gliemann
Department of Medical Biochemistry, University of Aarhus, Denmark.

The endocytic alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP) binds several classes of extracellular ligands at independent sites. In addition, alpha 2MR/LRP can bind multiple copies of the 39-40-kDa receptor-associated protein (RAP). Both amino-terminal and carboxyl-terminal fragments of RAP exhibit affinity, and the fragments apparently bind to different sites on the receptor. RAP completely inhibits the binding of all presently known extracellular ligands, whereas several ligands such as alpha 2-macroglobulin and tissue-type plasminogen activator are poor inhibitors of RAP binding. Since RAP is largely an intracellular molecule that normally does not occupy alpha 2MR/LRP at the cell surface, we hypothesized that an established extracellular ligand might bind to those sites on the receptor capable of binding the RAP fragments. We found complete cross-competition between carboxyl-terminal RAP fragments and fragments of lipoprotein lipase containing the recently identified binding domain for alpha 2MR/LRP (Nykjaer, A., Nielsen, M., Lookene, A., Meyer, N., Røigaard, H., Etzerodt, M., Beisiegel, U., Olivecrona, G., and Gliemann, J. (1994) J. Biol. Chem. 269, 31747-31755). Moreover, the lipoprotein lipase fragment completely inhibited the binding of several alpha 2MR/LRP ligands in a pattern similar to that of carboxyl-terminal RAP fragments. On the other hand, the amino-terminal RAP fragment was a poor competitor of binding of the lipoprotein lipase fragment, whereas it competed effectively with pro-uPA for binding to the receptor. The results provide evidence that lipoprotein lipase binds to the site on alpha2MR/LRP also available for binding of the carboxyl-terminal domain of RAP and suggest that pro-uPA may bind to or overlap the site available for the amino-terminal domain of RAP.

UI MeSH Term Description Entries
D008071 Lipoprotein Lipase An enzyme of the hydrolase class that catalyzes the reaction of triacylglycerol and water to yield diacylglycerol and a fatty acid anion. The enzyme hydrolyzes triacylglycerols in chylomicrons, very-low-density lipoproteins, low-density lipoproteins, and diacylglycerols. It occurs on capillary endothelial surfaces, especially in mammary, muscle, and adipose tissue. Genetic deficiency of the enzyme causes familial hyperlipoproteinemia Type I. (Dorland, 27th ed) EC 3.1.1.34. Heparin-Clearing Factor,Lipemia-Clearing Factor,Diacylglycerol Lipase,Diglyceride Lipase,Post-Heparin Lipase,Postheparin Lipase,Postheparin Lipoprotein Lipase,Factor, Heparin-Clearing,Factor, Lipemia-Clearing,Heparin Clearing Factor,Lipase, Diacylglycerol,Lipase, Diglyceride,Lipase, Lipoprotein,Lipase, Post-Heparin,Lipase, Postheparin,Lipase, Postheparin Lipoprotein,Lipemia Clearing Factor,Lipoprotein Lipase, Postheparin,Post Heparin Lipase
D008969 Molecular Sequence Data Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories. Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D010446 Peptide Fragments Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques. Peptide Fragment,Fragment, Peptide,Fragments, Peptide
D011971 Receptors, Immunologic Cell surface molecules on cells of the immune system that specifically bind surface molecules or messenger molecules and trigger changes in the behavior of cells. Although these receptors were first identified in the immune system, many have important functions elsewhere. Immunologic Receptors,Immunologic Receptor,Immunological Receptors,Receptor, Immunologic,Receptors, Immunological
D011973 Receptors, LDL Receptors on the plasma membrane of nonhepatic cells that specifically bind LDL. The receptors are localized in specialized regions called coated pits. Hypercholesteremia is caused by an allelic genetic defect of three types: 1, receptors do not bind to LDL; 2, there is reduced binding of LDL; and 3, there is normal binding but no internalization of LDL. In consequence, entry of cholesterol esters into the cell is impaired and the intracellular feedback by cholesterol on 3-hydroxy-3-methylglutaryl CoA reductase is lacking. LDL Receptors,Lipoprotein LDL Receptors,Receptors, Low Density Lipoprotein,LDL Receptor,LDL Receptors, Lipoprotein,Low Density Lipoprotein Receptor,Low Density Lipoprotein Receptors,Receptors, Lipoprotein, LDL,Receptor, LDL,Receptors, Lipoprotein LDL
D011994 Recombinant Proteins Proteins prepared by recombinant DNA technology. Biosynthetic Protein,Biosynthetic Proteins,DNA Recombinant Proteins,Recombinant Protein,Proteins, Biosynthetic,Proteins, Recombinant DNA,DNA Proteins, Recombinant,Protein, Biosynthetic,Protein, Recombinant,Proteins, DNA Recombinant,Proteins, Recombinant,Recombinant DNA Proteins,Recombinant Proteins, DNA
D004792 Enzyme Precursors Physiologically inactive substances that can be converted to active enzymes. Enzyme Precursor,Proenzyme,Proenzymes,Zymogen,Zymogens,Precursor, Enzyme,Precursors, Enzyme
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000511 alpha-Macroglobulins Glycoproteins with a molecular weight of approximately 620,000 to 680,000. Precipitation by electrophoresis is in the alpha region. They include alpha 1-macroglobulins and alpha 2-macroglobulins. These proteins exhibit trypsin-, chymotrypsin-, thrombin-, and plasmin-binding activity and function as hormonal transporters. Slow alpha 2-Macroglobulins,alpha 2-Acute Phase Globulins,alpha-Macrofetoproteins,45S RNP,Acute-Phase alpha 1-Protein,Slow alpha 2-Globulin,alpha 1-Acute Phase Globulin,alpha 1-Acute Phase Protein,alpha 1-Macroglobulin,alpha 2-Acute Phase Globulin,alpha-Macrofetoprotein,Acute Phase alpha 1 Protein,RNP, 45S,Slow alpha 2 Globulin,Slow alpha 2 Macroglobulins,alpha 1 Acute Phase Globulin,alpha 1 Acute Phase Protein,alpha 1 Macroglobulin,alpha 1-Protein, Acute-Phase,alpha 2 Acute Phase Globulin,alpha 2 Acute Phase Globulins,alpha 2-Globulin, Slow,alpha 2-Macroglobulins, Slow,alpha Macrofetoprotein,alpha Macrofetoproteins,alpha Macroglobulins
D000595 Amino Acid Sequence The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION. Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein

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