Characterization of the Heparin Binding Sites in Human Apolipoprotein E
Apolipoprotein (apo) E mediates lipoprotein remnant clearance via interaction with cell-surface heparan sulfate proteoglycans. Both the 22-kDa N-terminal domain and 10-kDa C-terminal domain of apoE contain a heparin binding site; the N-terminal site overlaps with the low density lipoprotein receptor binding region and the C-terminal site is undefined. To understand the molecular details of the apoE-heparin interaction, we defined the microenvironments of all 12 lysine residues in intact apoE3 and examined their relative contributions to heparin binding. Nuclear magnetic resonance measurements showed that, in apoE3-dimyristoyl phosphatidylcholine discs, Lys-143 and -146 in the N-terminal domain and Lys-233 in the C-terminal domain have unusually low pKa values, indicating high positive electrostatic potential around these residues. Binding experiments using heparin-Sepharose gel demonstrated that the lipid-free 10-kDa fragment interacted strongly with heparin and a point mutation K233Q largely abolished the binding, indicating that Lys-233 is involved in heparin binding and that an unusually basic lysine microenvironment is critical for the interaction with heparin. With lipidated apoE3, it is confirmed that the Lys-233 site is completely masked and the N-terminal site mediates heparin binding. In addition, mutations of the two heparin binding sites in intact apoE3 demonstrated the dominant role of the N-terminal site in the heparin binding of apoE even in the lipid-free state. These results suggest that apoE interacts predominately with cell-surface heparan sulfate proteoglycans through the N-terminal binding site. However, Lys-233 may be involved in the binding of apoE to certain cell-surface sites, such as the protein core of biglycan. Apolipoprotein (apo) E mediates lipoprotein remnant clearance via interaction with cell-surface heparan sulfate proteoglycans. Both the 22-kDa N-terminal domain and 10-kDa C-terminal domain of apoE contain a heparin binding site; the N-terminal site overlaps with the low density lipoprotein receptor binding region and the C-terminal site is undefined. To understand the molecular details of the apoE-heparin interaction, we defined the microenvironments of all 12 lysine residues in intact apoE3 and examined their relative contributions to heparin binding. Nuclear magnetic resonance measurements showed that, in apoE3-dimyristoyl phosphatidylcholine discs, Lys-143 and -146 in the N-terminal domain and Lys-233 in the C-terminal domain have unusually low pKa values, indicating high positive electrostatic potential around these residues. Binding experiments using heparin-Sepharose gel demonstrated that the lipid-free 10-kDa fragment interacted strongly with heparin and a point mutation K233Q largely abolished the binding, indicating that Lys-233 is involved in heparin binding and that an unusually basic lysine microenvironment is critical for the interaction with heparin. With lipidated apoE3, it is confirmed that the Lys-233 site is completely masked and the N-terminal site mediates heparin binding. In addition, mutations of the two heparin binding sites in intact apoE3 demonstrated the dominant role of the N-terminal site in the heparin binding of apoE even in the lipid-free state. These results suggest that apoE interacts predominately with cell-surface heparan sulfate proteoglycans through the N-terminal binding site. However, Lys-233 may be involved in the binding of apoE to certain cell-surface sites, such as the protein core of biglycan. apolipoprotein heparan sulfate proteoglycan heteronuclear single quantum coherence low density lipoprotein LDL receptor-related protein 1,2-dimyristoyl phosphatidylcholine 1-palmitoyl-2-oleoyl phosphatidylcholine nuclear magnetic resonance Apolipoprotein E (apoE)1is a critical ligand for several hepatic lipoprotein receptors, including the low density lipoprotein (LDL) receptor and the LDL receptor-related protein (LRP), and for cell-surface heparan sulfate proteoglycans (HSPG) (1Mahley R.W. Science. 1988; 240: 622-630Crossref PubMed Scopus (3353) Google Scholar, 2Weisgraber K.H. Adv. Protein Chem. 1994; 45: 249-302Crossref PubMed Google Scholar, 3Mahley R.W. Rall Jr., S.C. Annu. Rev. Genomics Hum. Genet. 2000; 1: 507-537Crossref PubMed Scopus (1304) Google Scholar). Through its interaction with these receptors and with the HSPG-LRP pathway, apoE mediates the catabolism of remnant lipoproteins (4Cooper A.D. J. Lipid Res. 1997; 38: 2173-2192Abstract Full Text PDF PubMed Google Scholar, 5Mahley R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar). In the HSPG-LRP pathway, apoE is postulated to interact initially with cell-surface HSPG and then to transfer to the LRP for internalization (6Ji Z.S. Fazio S. Lee Y.L. Mahley R.W. J. Biol. Chem. 1994; 269: 2764-2772Abstract Full Text PDF PubMed Google Scholar, 7Mahley R.W. Isr. J. Med. Sci. 1996; 32: 414-429PubMed Google Scholar). Therefore, the interaction of apoE with HSPG is an initial step in the clearance of apoE-containing lipoproteins from the plasma. The apoE-HSPG interaction is also involved in the differential effects of the apoE isoforms on neurite outgrowth (8Holtzman D.M. Pitas R.E. Kilbridge J. Nathan B. Mahley R.W. Bu G. Schwartz A.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 9480-9484Crossref PubMed Scopus (327) Google Scholar, 9Ji Z.S. Pitas R.E. Mahley R.W. J. Biol. Chem. 1998; 273: 13452-13460Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar), the existence of a pool of newly secreted apoE on the cell surface (10Lucas M. Mazzone T. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, Y.L. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar, Mazzone T. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar), and the of cell J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In addition, several suggest that binding of apoE to HSPG may be involved in R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar, K.H. Mahley R.W. J. 1996; PubMed Scopus Google G. 2000; PubMed Scopus Google a single two a 22-kDa N-terminal domain and a 10-kDa C-terminal domain K.H. Adv. Protein Chem. 1994; 45: 249-302Crossref PubMed Google Scholar, K.H. J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar). The N-terminal domain in the lipid-free as a of and the LDL receptor binding region in K.H. Mahley R.W. Science. PubMed Scopus Google Scholar). The of the residues is critical for binding to the LDL receptor M. K.H. S. J. Lipid Res. 2000; Full Text Full Text PDF PubMed Google Scholar). using nuclear magnetic resonance demonstrated that Lys-143 and have unusually low pKa of in positive electrostatic potential with the region residues S. M. S. K.H. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, S. S. M. K.H. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar). The C-terminal domain is also to be a and the binding region K.H. J. Biol. Chem. Full Text PDF PubMed Google Scholar, S.C. Adv. Protein Chem. 1994; 45: PubMed Google Scholar). The molecular of the in the C-terminal domain and C-terminal contain a heparin binding site A.D. Res. PubMed Scopus Google K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The N-terminal domain site is residues and overlaps with the receptor binding region K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). In the HSPG binding of apoE is mutations of and indicating that these basic residues to heparin binding Z.S. Fazio S. Mahley R.W. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). on the interaction a and the N-terminal domain of that and with sulfate from the fragment J. K.H. B. 40: PubMed Scopus Google Scholar), with a binding of and for HSPG Z.S. Fazio S. Mahley R.W. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). also the heparin fragment and and a showed that and for binding to with in an interaction with the heparin fragment and Lys-143 in a S. S. K.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google of the to the heparin binding site in the C-terminal domain of apoE and to its to the apoE-heparin interaction in lipid-free and lipidated demonstrated that the C-terminal domain to heparin with the N-terminal domain in the lipid-free and that an basic microenvironment around Lys-233 is involved in heparin binding. C-terminal site is for heparin binding in the lipid-free and lipidated of the intact apoE that the N-terminal site to the interaction of apoE with interaction apoE and HSPG is in several such as lipoprotein remnant clearance R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar, Z.S. Mahley R.W. J. Biol. Chem. Full Text PDF PubMed Google and neurite outgrowth R.W. Rall Jr., S.C. Annu. Rev. Genomics Hum. Genet. 2000; 1: 507-537Crossref PubMed Scopus (1304) Google Scholar, K.H. Mahley R.W. J. 1996; PubMed Scopus Google Scholar). two heparin binding sites residues and in the N-terminal receptor binding region K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google and defined sites in the C-terminal binding region A.D. Res. PubMed Scopus Google Scholar, K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The N-terminal site using 22-kDa and an heparin and site involved in the interaction with the heparin fragment S. S. K.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In using we Lys-233 as a lysine in the C-terminal site and also the relative contributions of sites to the heparin binding of using apoE that residues A.D. Res. PubMed Scopus Google and K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google contain heparin binding The site is a in the binding of the C-terminal 10-kDa fragment to heparin it is in is also in the fragment to heparin the residues A.D. Res. PubMed Scopus Google its is from it is as of the apoE is that Lys-233 is of the heparin binding site a with an residues K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google the of the may with the of results that all 12 of apoE3, Lys-143 and -146 in the N-terminal domain and Lys-233 in the C-terminal domain have unusually low pKa values, of high positive electrostatic potential around these residues. showed that positive electrostatic potential around Lys-143 and -146 is involved in the binding of the N-terminal domain of apoE to the LDL receptor and heparin. In we demonstrated that Lys-233 is critical for the heparin binding of the C-terminal domain indicating that an unusually basic lysine microenvironment in the C-terminal domain is also involved in the heparin In an the basic residues and two of the is that several residues in the on the of the the positive electrostatic potential around the of of the heparin binding of apoE3 and its and 10-kDa In the lipid-free the 10-kDa fragment to heparin with the 22-kDa fragment In the heparin binding of the 10-kDa fragment completely abolished with with that the C-terminal site is for interaction in the lipid-free K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. K.H. J. Lipid Res. 2000; Full Text Full Text PDF PubMed Google Scholar). The C-terminal domain of apoE a and is for of apoE in the N-terminal domain is K.H. J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar). Therefore, the interaction of the C-terminal domain with heparin to be of its in the heparin binding of the apoE3 is in is that of apoE3 and is with that of the 22-kDa indicating that through the C-terminal domain is for the heparin binding of the lipid-free of heparin binding heparin binding through effects A. B. T. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). of the receptor binding domain for the high interaction of apoE with the LDL receptor T. S. A. J. PubMed Scopus Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar). In the binding of apoE3 and the 22-kDa fragment in may be the in from of the N-terminal domain the heparin binding of the 10-kDa the C-terminal site of apoE3 to be involved in the heparin binding of lipid-free in in heparin binding the lipid-free apoE3, and that, even in the lipid-free the N-terminal site is involved in the heparin interaction of is the C-terminal site of the lipid-free apoE is to interaction with heparin. is that the heparin interaction of the C-terminal domain is the region as a the two the the 10-kDa domain and the to heparin interaction the 10-kDa domain and the region the C-terminal heparin binding site basic residues around interaction with heparin. resonance transfer of apoE3 the and the C-terminal in the lipid-free with the region the N-terminal domain to the C-terminal domain J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google high density lipoproteins to the in and apoE is to as a that these in M. A. 1998; PubMed Scopus Google Scholar). binding interaction apoE and to via the C-terminal domain in the lysine and residues and involved in the binding M. K.H. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, S. A. Biol. PubMed Scopus Google Scholar). The results of the suggest that the unusually basic microenvironment around Lys-233 to the demonstrated that C-terminal of apoE with in the M. B. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, Res. 1997; PubMed Scopus Google and that of apoE in T. Mahley R.W. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The of apoE in the that the C-terminal fragment may to interaction with HSPG in the we have the heparin binding site of the C-terminal domain of that the basic residues around lysine critical for the heparin binding of the C-terminal domain for heparin binding in apoE even in the lipid-free state. it that apoE with cell surface HSPG through the N-terminal the C-terminal domain for binding to lipoprotein Apolipoprotein E (apoE)1is a critical ligand for several hepatic lipoprotein receptors, including the low density lipoprotein (LDL) receptor and the LDL receptor-related protein (LRP), and for cell-surface heparan sulfate proteoglycans (HSPG) (1Mahley R.W. Science. 1988; 240: 622-630Crossref PubMed Scopus (3353) Google Scholar, 2Weisgraber K.H. Adv. Protein Chem. 1994; 45: 249-302Crossref PubMed Google Scholar, 3Mahley R.W. Rall Jr., S.C. Annu. Rev. Genomics Hum. Genet. 2000; 1: 507-537Crossref PubMed Scopus (1304) Google Scholar). Through its interaction with these receptors and with the HSPG-LRP pathway, apoE mediates the catabolism of remnant lipoproteins (4Cooper A.D. J. Lipid Res. 1997; 38: 2173-2192Abstract Full Text PDF PubMed Google Scholar, 5Mahley R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar). In the HSPG-LRP pathway, apoE is postulated to interact initially with cell-surface HSPG and then to transfer to the LRP for internalization (6Ji Z.S. Fazio S. Lee Y.L. Mahley R.W. J. Biol. Chem. 1994; 269: 2764-2772Abstract Full Text PDF PubMed Google Scholar, 7Mahley R.W. Isr. J. Med. Sci. 1996; 32: 414-429PubMed Google Scholar). Therefore, the interaction of apoE with HSPG is an initial step in the clearance of apoE-containing lipoproteins from the plasma. The apoE-HSPG interaction is also involved in the differential effects of the apoE isoforms on neurite outgrowth (8Holtzman D.M. Pitas R.E. Kilbridge J. Nathan B. Mahley R.W. Bu G. Schwartz A.L. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 9480-9484Crossref PubMed Scopus (327) Google Scholar, 9Ji Z.S. Pitas R.E. Mahley R.W. J. Biol. Chem. 1998; 273: 13452-13460Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar), the existence of a pool of newly secreted apoE on the cell surface (10Lucas M. Mazzone T. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, Y.L. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar, Mazzone T. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar), and the of cell J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In addition, several suggest that binding of apoE to HSPG may be involved in R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar, K.H. Mahley R.W. J. 1996; PubMed Scopus Google G. 2000; PubMed Scopus Google Scholar). a single two a 22-kDa N-terminal domain and a 10-kDa C-terminal domain K.H. Adv. Protein Chem. 1994; 45: 249-302Crossref PubMed Google Scholar, K.H. J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar). The N-terminal domain in the lipid-free as a of and the LDL receptor binding region in K.H. Mahley R.W. Science. PubMed Scopus Google Scholar). The of the residues is critical for binding to the LDL receptor M. K.H. S. J. Lipid Res. 2000; Full Text Full Text PDF PubMed Google Scholar). using nuclear magnetic resonance demonstrated that Lys-143 and have unusually low pKa of in positive electrostatic potential with the region residues S. M. S. K.H. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, S. S. M. K.H. J. Lipid Res. Full Text Full Text PDF PubMed Google Scholar). The C-terminal domain is also to be a and the binding region K.H. J. Biol. Chem. Full Text PDF PubMed Google Scholar, S.C. Adv. Protein Chem. 1994; 45: PubMed Google Scholar). The molecular of the in the C-terminal domain The and C-terminal contain a heparin binding site A.D. Res. PubMed Scopus Google K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The N-terminal domain site is residues and overlaps with the receptor binding region K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). In the HSPG binding of apoE is mutations of and indicating that these basic residues to heparin binding Z.S. Fazio S. Mahley R.W. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). on the interaction a and the N-terminal domain of that and with sulfate from the fragment J. K.H. B. 40: PubMed Scopus Google Scholar), with a binding of and for HSPG Z.S. Fazio S. Mahley R.W. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). also the heparin fragment and and a showed that and for binding to with in an interaction with the heparin fragment and Lys-143 in a S. S. K.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The of the to the heparin binding site in the C-terminal domain of apoE and to its to the apoE-heparin interaction in lipid-free and lipidated demonstrated that the C-terminal domain to heparin with the N-terminal domain in the lipid-free and that an basic microenvironment around Lys-233 is involved in heparin binding. C-terminal site is for heparin binding in the lipid-free and lipidated of the intact apoE that the N-terminal site to the interaction of apoE with interaction apoE and HSPG is in several such as lipoprotein remnant clearance R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar, Z.S. Mahley R.W. J. Biol. Chem. Full Text PDF PubMed Google and neurite outgrowth R.W. Rall Jr., S.C. Annu. Rev. Genomics Hum. Genet. 2000; 1: 507-537Crossref PubMed Scopus (1304) Google Scholar, K.H. Mahley R.W. J. 1996; PubMed Scopus Google Scholar). two heparin binding sites residues and in the N-terminal receptor binding region K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google and defined sites in the C-terminal binding region A.D. Res. PubMed Scopus Google Scholar, K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The N-terminal site using 22-kDa and an heparin and site involved in the interaction with the heparin fragment S. S. K.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In using we Lys-233 as a lysine in the C-terminal site and also the relative contributions of sites to the heparin binding of using apoE that residues A.D. Res. PubMed Scopus Google and K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google contain heparin binding The site is a in the binding of the C-terminal 10-kDa fragment to heparin it is in is also in the fragment to heparin the residues A.D. Res. PubMed Scopus Google its is from it is as of the apoE is that Lys-233 is of the heparin binding site a with an residues K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google the of the may with the of results that all 12 of apoE3, Lys-143 and -146 in the N-terminal domain and Lys-233 in the C-terminal domain have unusually low pKa values, of high positive electrostatic potential around these residues. showed that positive electrostatic potential around Lys-143 and -146 is involved in the binding of the N-terminal domain of apoE to the LDL receptor and heparin. In we demonstrated that Lys-233 is critical for the heparin binding of the C-terminal domain indicating that an unusually basic lysine microenvironment in the C-terminal domain is also involved in the heparin In an the basic residues and two of the is that several residues in the on the of the the positive electrostatic potential around the of of the heparin binding of apoE3 and its and 10-kDa In the lipid-free the 10-kDa fragment to heparin with the 22-kDa fragment In the heparin binding of the 10-kDa fragment completely abolished with with that the C-terminal site is for interaction in the lipid-free K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. K.H. J. Lipid Res. 2000; Full Text Full Text PDF PubMed Google Scholar). The C-terminal domain of apoE a and is for of apoE in the N-terminal domain is K.H. J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar). Therefore, the interaction of the C-terminal domain with heparin to be of its in the heparin binding of the apoE3 is in is that of apoE3 and is with that of the 22-kDa indicating that through the C-terminal domain is for the heparin binding of the lipid-free of heparin binding heparin binding through effects A. B. T. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). of the receptor binding domain for the high interaction of apoE with the LDL receptor T. S. A. J. PubMed Scopus Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar). In the binding of apoE3 and the 22-kDa fragment in may be the in from of the N-terminal domain the heparin binding of the 10-kDa the C-terminal site of apoE3 to be involved in the heparin binding of lipid-free in in heparin binding the lipid-free apoE3, and that, even in the lipid-free the N-terminal site is involved in the heparin interaction of is the C-terminal site of the lipid-free apoE is to interaction with heparin. is that the heparin interaction of the C-terminal domain is the region as a the two the the 10-kDa domain and the to heparin interaction the 10-kDa domain and the region the C-terminal heparin binding site basic residues around interaction with heparin. resonance transfer of apoE3 the and the C-terminal in the lipid-free with the region the N-terminal domain to the C-terminal domain J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google high density lipoproteins to the in and apoE is to as a that these in M. A. 1998; PubMed Scopus Google Scholar). binding interaction apoE and to via the C-terminal domain in the lysine and residues and involved in the binding M. K.H. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, S. A. Biol. PubMed Scopus Google Scholar). The results of the suggest that the unusually basic microenvironment around Lys-233 to the demonstrated that C-terminal of apoE with in the M. B. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, Res. 1997; PubMed Scopus Google and that of apoE in T. Mahley R.W. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The of apoE in the that the C-terminal fragment may to interaction with HSPG in the we have the heparin binding site of the C-terminal domain of that the basic residues around lysine critical for the heparin binding of the C-terminal domain for heparin binding in apoE even in the lipid-free state. it that apoE with cell surface HSPG through the N-terminal the C-terminal domain for binding to lipoprotein The interaction apoE and HSPG is in several such as lipoprotein remnant clearance R.W. Ji Z.S. J. Lipid Res. 1999; 40: 1-16Abstract Full Text Full Text PDF PubMed Google Scholar, Z.S. Mahley R.W. J. Biol. Chem. Full Text PDF PubMed Google and neurite outgrowth R.W. Rall Jr., S.C. Annu. Rev. Genomics Hum. Genet. 2000; 1: 507-537Crossref PubMed Scopus (1304) Google Scholar, K.H. Mahley R.W. J. 1996; PubMed Scopus Google Scholar). two heparin binding sites residues and in the N-terminal receptor binding region K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google and defined sites in the C-terminal binding region A.D. Res. PubMed Scopus Google Scholar, K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The N-terminal site using 22-kDa and an heparin and site involved in the interaction with the heparin fragment S. S. K.H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In using we Lys-233 as a lysine in the C-terminal site and also the relative contributions of sites to the heparin binding of using apoE that residues A.D. Res. PubMed Scopus Google and K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google contain heparin binding The site is a in the binding of the C-terminal 10-kDa fragment to heparin it is in is also in the fragment to heparin the residues A.D. Res. PubMed Scopus Google its is from it is as of the apoE is that Lys-233 is of the heparin binding site a with an residues K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google the of the may with the of results that all 12 of apoE3, Lys-143 and -146 in the N-terminal domain and Lys-233 in the C-terminal domain have unusually low pKa values, of high positive electrostatic potential around these residues. showed that positive electrostatic potential around Lys-143 and -146 is involved in the binding of the N-terminal domain of apoE to the LDL receptor and heparin. In we demonstrated that Lys-233 is critical for the heparin binding of the C-terminal domain indicating that an unusually basic lysine microenvironment in the C-terminal domain is also involved in the heparin In an the basic residues and two of the is that several residues in the on the of the the positive electrostatic potential around the of of the heparin binding of apoE3 and its and 10-kDa In the lipid-free the 10-kDa fragment to heparin with the 22-kDa fragment In the heparin binding of the 10-kDa fragment completely abolished with with that the C-terminal site is for interaction in the lipid-free K.H. Rall Jr., S.C. Mahley R.W. R.W. Y.L. J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. K.H. J. Lipid Res. 2000; Full Text Full Text PDF PubMed Google Scholar). The C-terminal domain of apoE a and is for of apoE in the N-terminal domain is K.H. J. Biol. Chem. 1988; Full Text PDF PubMed Google Scholar). Therefore, the interaction of the C-terminal domain with heparin to be of its in the heparin binding of the apoE3 is in is that of apoE3 and is with that of the 22-kDa indicating that through the C-terminal domain is for the heparin binding of the lipid-free of heparin binding heparin binding through effects A. B. T. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). of the receptor binding domain for the high interaction of apoE with the LDL receptor T. S. A. J. PubMed Scopus Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar). In the binding of apoE3 and the 22-kDa fragment in may be the in from of the N-terminal domain the heparin binding of the 10-kDa the C-terminal site of apoE3 to be involved in the heparin binding of lipid-free in in heparin binding the lipid-free apoE3, and that, even in the lipid-free the N-terminal site is involved in the heparin interaction of is the C-terminal site of the lipid-free apoE is to interaction with heparin. is that the heparin interaction of the C-terminal domain is the region as a the two the the 10-kDa domain and the to heparin interaction the 10-kDa domain and the region the C-terminal heparin binding site basic residues around interaction with heparin. resonance transfer of apoE3 the and the C-terminal in the lipid-free with the region the N-terminal domain to the C-terminal domain J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). high density lipoproteins to the in and apoE is to as a that these in M. A. 1998; PubMed Scopus Google Scholar). binding interaction apoE and to via the C-terminal domain in the lysine and residues and involved in the binding M. K.H. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, S. A. Biol. PubMed Scopus Google Scholar). The results of the suggest that the unusually basic microenvironment around Lys-233 to the demonstrated that C-terminal of apoE with in the M. B. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, Res. 1997; PubMed Scopus Google and that of apoE in T. Mahley R.W. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The of apoE in the that the C-terminal fragment may to interaction with HSPG in the In we have the heparin binding site of the C-terminal domain of that the basic residues around lysine critical for the heparin binding of the C-terminal domain for heparin binding in apoE even in the lipid-free state. it that apoE with cell surface HSPG through the N-terminal the C-terminal domain for binding to lipoprotein