Role of the N- and C-terminal domains in binding of apolipoprotein E isoforms to heparan sulfate and dermatan sulfate: a surface plasmon resonance study.
The ability of apolipoprotein E (apoE) to bind to cell-surface glycosaminoglycans (GAGs) is important for lipoprotein remnant catabolism. Using surface plasmon resonance, we previously showed that the binding of apoE to heparin is a two-step process; the initial binding involves fast electrostatic interaction, followed by a slower hydrophobic interaction. Here we examined the contributions of the N- and C-terminal domains to each step of the binding of apoE isoforms to heparan sulfate (HS) and dermatan sulfate (DS). ApoE3 bound to less sulfated HS and DS with a decreased favorable free energy of binding in the first step compared to heparin, indicating that the degree of sulfation has a major effect on the electrostatic interaction of GAGs with apoE. Mutation of a key Lys residue in the N-terminal heparin binding site of apoE significantly affected this electrostatic interaction. Progressive truncation of the C-terminal alpha-helical regions which favors the monomeric form of apoE3 greatly weakened the ability of apoE3 to bind to HS, with a much reduced favorable free energy of binding of the first step, suggesting that the C-terminal domain contributes to the GAG binding of apoE by the oligomerization effect. In agreement with this, dimerization of the apoE3 N-terminal fragment via disulfide linkage restored the electrostatic interaction of apoE with HS. Significantly, apoE4 exhibited much stronger binding to HS and DS than apoE2 or apoE3 in both lipid-free and lipidated states, perhaps resulting from enhanced electrostatic interaction through the N-terminal domain. This isoform difference in GAG binding of apoE may be physiologically significant such as in the retention of apoE-containing lipoproteins in the arterial wall.
Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501, Japan.
Yuko
Y
Yamauchi
Noriko
N
Deguchi
Chika
C
Takagi
Masafumi
M
Tanaka
Padmaja
P
Dhanasekaran
Minoru
M
Nakano
Tetsurou
T
Handa
Michael C
MC
Phillips
Sissel
S
Lund-Katz
Hiroyuki
H
Saito
D000818:Animals; D053318:Apolipoprotein E3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D053327:Apolipoprotein E4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001057:Apolipoproteins E / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002942:Circular Dichroism; D003871:Dermatan Sulfate / Q000737:chemistry / Q000378:metabolism*; D004220:Disulfides / Q000737:chemistry; D006497:Heparan Sulfate / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D055672:Static Electricity; D020349:Surface Plasmon Resonance / Q000379:methods*; D013552:Swine
D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D003871:Dermatan Sulfate; D004220:Disulfides; D006497:Heparan Sulfate; D008239:Lysine