Interaction of apolipoprotein AII with the putative high-density lipoprotein receptor.
1993
Vadiveloo P.K. | Allan C.M. | Murray B.J. | Fidge N.H.
There is strong evidence to indicate that binding of HDL by cells is due to recognition of apoproteins residing on the surface of the lipoprotein by the putative HDL receptor(s). Although both of the major HDL apoproteins, AI and AII, are recognized by the putative receptor, the nature of the binding interaction and the domains of the apoproteins involved are largely unknown. Previous data from this laboratory led to the proposal of a model to explain how HDL particles containing AII interacted with the HDL receptor in a different manner as compared to HDL particles which contain apoAI but not apoAII [Vadiveloo, P.K., and Fidge, N.H. (1992) Biochem. J. 284,145-151]. The model predicted that each chain of the apoAII homodimer contained a binding domain capable of interacting with the HDL receptor. This model was tested in the current study by preparing apoAII monomers, complexing them with phospholipid, and determining the ability of these complexes to bind to putative HDL receptors in rat liver plasma membranes (RLPM) and bovine aortic endothelial cell membranes (BAECM) by ligand blotting. The data showed that these complexes were bound by HB1 and HB2 from RLPM, and to the 110-kDa HDL binding protein from BAECM, providing critical evidence to support the model. Further investigation into the binding interaction revealed that apoAII complexed with phospholipid (ApoAII-PC) bound more than delipidated apoAII, which bound more than delipidated apoAII monomers. Thus, optimum binding required the presence of lipid. Since the amount of binding correlated with the amount of alpha-helical content of the molecules (i.e., apoAII-PC > delipidated apoAII > delipidated apoAII monomers), these findings are consistent with the hypothesis that alpha-helical regions are involved in recognition of apoAII by the putative HDL receptor. ApoAII has a single methionine residue at position 26.
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