Apolipoprotein(a) Binds via Its C-terminal Domain to the Protein Core of the Proteoglycan Decorin

Abstract

Although it is known that lipoprotein(a) (Lp(a)) binds to proteoglycans, the mechanism for this binding has not been fully elucidated. In order to shed light on this subject, we examined the interactions of decorin, a proteoglycan with a well defined protein core and a single glycosaminoglycan (GAG) chain, with Lp(a) and derivatives, namely Lp(a) deprived of apo(a), or Lp(a؊), free apo(a), and the two main proteolytic fragments, F1 and F2. By circular dichroism criteria, the decorin preparations used had the same secondary structure as that previously reported for native decorin. Authentic low density lipoprotein from the same human donor was used as a control. In a solid phase system, Lp(a؊)and low density lipoprotein bound to decorin in a comparable manner. This binding required Ca 2؉ /Mg 2؉ ions, was lysine-mediated, and was markedly decreased in the presence of GAG-depleted decorin, suggesting the ionic nature of the interaction likely involving apoB100 and the GAG component of decorin. Free apo(a) also bound to decorin; however, the binding was neither cation-dependent nor lysine-mediated, unaffected by sialic acid depletion of apo(a), and markedly decreased when either reduced and alkylated apo(a) or reduced and alkylated decorin was used in the assay. Of note, the binding of apo(a) was unaffected when it was incubated with a spectrally native decorin that had been renatured from either 4 M guanidine hydrochloride by extensive dialysis or cooled from 65 to 25°C. On the other hand, the binding significantly increased when decorin was depleted of GAGs, which by themselves had no affinity for apo(a). The binding of apo(a) to the decorin protein core was also elicited by the C-terminal domain of apo(a), and it was favored by high NaCl concentrations, 1 to 2 M. No binding was exhibited by the N-terminal domain accounting for the lack of effect of apo(a) size polymorphism on the binding. In the case of whole Lp(a), the binding to immobilized decorin was mostly GAGdependent and ionic in nature. A minor contribution by apo(a) was detected when GAG-depleted decorin was used in the assay. Our results indicate that the binding of Lp(a) to decorin involves interactions both electrostatic (apoB100-GAG) and hydrophobic (apo(a)-decorin protein core), and that the binding of apo(a) requires decorin protein core to be in its native state.

Macrophage Metalloelastase, MMP-12, Cleaves Human Apolipoprotein(a) in the Linker Region between Kringles IV-4 and IV-5

“…Because F1 and F2 are generated in vitro by the action of both NE (5) and MMP-12 on apo(a), one has to ask why only F1 was present in the plasma of the NE Ϫ/Ϫ and control mice injected intravenously with apo(a). This may be because of the fact that F2 but not F1 binds to matrix macromolecules such as fibrinogen and fibronectin (4) and as exemplified by our recent findings on the proteoglycan decorin (29). On the other hand, F1, for which no ligand has been identified thus far (30), once formed at tissue sites would be free to diffuse and return to the blood stream by a reverse flow process.…”

Decorin suppresses tumor cell-mediated angiogenesis

“…It is possible that this discrepancy derives from the use of guanidine HCl-extracted decorin in the studies mentioned above. Although it appears that proper re-folding of decorin occurs following removal of guanidine HCl, at least based on binding to collagen type I (Vogel et al, 1984) or apolipoprotein A (Klezovitch et al, 1998), it is our experience that even a simple freezing and thawing can abrogate some of the functional properties of decorin, such as interaction with the EGFR or MAP kinase activation (Csorda´s et al, 2000;Santra et al, 2000). In addition, the culture conditions of our study differed from those reported earlier (de Lange Davies et al, 2001;Kinsella et al, 2000).…”

Difference in the Risk Factors for Coronary, Renal and Other Peripheral Arteriosclerosis in Heterozygous Familial Hypercholesterolemia

“…28 Lp(a), which is known to be a highly atherogenic lipoprotein having a protein moiety apoB100 disulfide, binds to proteoglycans. 29 Degradation of endothelial heparan sulfate proteoglycan by homocysteine is considered to cause a loss of ability to protect the endothelial cell surface from oxidative stress. 30 Previous studies have shown that differences in expression of the proteoglycan of the arterial wall affects the subendothelial retention of atherogenic lipoproteins, including remnant particles.…”