Specificity of serine proteinase/serpin complex binding to very-low-density lipoprotein receptor and alpha2-macroglobulin receptor/low-density-lipoprotein-receptor-related protein.
Very-low-density lipoprotein receptor (VLDLR) and alpha2-macroglobulin receptor/low-density-lipoprotein-receptor-related protein (alpha2MR/LRP) are multifunctional endocytosis receptors of the low-density lipoprotein receptor family. Both have been shown to mediate endocytosis and degradation of complex between plasminogen activators and type-1 plasminogen-activator inhibitor (PAI-1) by cultured cells. We have now studied the specificity of binding and endocytosis by VLDLR and alpha2MR/LRP among a variety of serine proteinase/serpin complexes, including various combinations of the serine proteinases urokinase-type and tissue-type plasminogen activators, plasmin, thrombin, human leukocyte elastase, cathepsin G, and plasma kallikrein with the serpins PAI-1, horse leukocyte elastase inhibitor, protein C inhibitor, C1-inhibitor, alpha2-antiplasmin, alpha1-proteinase inhibitor, alpha1-antichymotrypsin, protease nexin-1, heparin cofactor II, and antithrombin III. Binding was estimated with radiolabelled ligands in ligand blotting analysis and microtiter well assays. Endocytosis was estimated by measuring receptor-associated protein (RAP)-sensitive degradation of radiolabelled complexes by Chinese hamster ovary cells transfected with VLDLR cDNA and by COS-1 cells, which have a high endogenous expression of alpha2MR/LRP. We found that the receptors bind with high affinity to some, but not all, combinations of plasminogen activators and thrombin with PAI-1, protease nexin-1, protein C inhibitor, and antithrombin III, while complexes of many serine proteinases with their primary inhibitor, i.e. plasmin/alpha2-antiplasmin complex, do not bind, or bind with a very low affinity. Both the serine proteinase and the serpin moieties contribute to the binding specificity. The binding specificities of VLDLR and alpha2MR/LRP are overlapping, but not identical. The results suggest that VLDLR and alpha2MR/LRP have different biological functions by having different binding specificities as well as by being expressed by different cell types.
Kasza
A
A
Department of Molecular and Structural Biology, University of Aarhus, Denmark.
Petersen
H H
HH
Heegaard
C W
CW
Oka
K
K
Christensen
A
A
Dubin
A
A
Chan
L
L
Andreasen
P A
PA
D016564:Amyloid beta-Protein Precursor; D000818:Animals; D019556:COS Cells / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D006224:Cricetinae; D004705:Endocytosis; D006801:Humans; D007700:Kinetics; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism*; D058258:Serpin E2; D015843:Serpins / Q000378:metabolism*; D013379:Substrate Specificity; D013917:Thrombin / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017395:Plasminogen Activator Inhibitor 1; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D011994:Recombinant Proteins; C545486:SERPINE2 protein, human; D058258:Serpin E2; D015843:Serpins; C036053:VLDL receptor; D012697:Serine Endopeptidases; D013917:Thrombin; D014568:Urokinase-Type Plasminogen Activator