Abstract
The interaction of plasma phospholipid transfer protein (PLTP) with HDL has not been characterized in detail, although we have reported that the apoA-I/apoA-II molar ratio in the HDL particle influences PLTP-mediated HDL conversion, but not phospholipid transfer. The aim of this study was to examine whether PLTP binds apoA-I or apoA-II, and if this occurs, then determine the PLTP-binding domain of the apoA-I molecule. To study the PLTP/apolipoprotein interaction we used a solid phase ligand binding assay, the ELISA technique, and apoA-I and apoA-II affinity chromatography. PLTP bound to both apoA-I and apoA-II affinity columns, a finding subsequently utilized in the purification of PLTP. PLTP also bound to both apoA-I and apoA-II on ELISA plates in a concentration-dependent manner, and the binding could be displaced by preincubating the PLTP sample with purified apolipoproteins. To determine which portion of apoA-I is recognized by PLTP, we coated ELISA plates with either recombinant full-length apoA-I or three shortened apoA-I forms sequentially truncated from the C-terminus. To characterize the PLTP binding ability of the C-terminal region of apoA-I, we used both C-terminal CNBr-fragment and a synthetic C-terminal peptide of apoA-I. To further confirm the identity of the binding region, we probed the interaction with a polyclonal and several monoclonal anti-apoA-I antibodies. The antibodies that inhibited the interaction between PLTP and apoA-I were directed towards apoA-I epitopes localized between amino acids 27–141. The polyclonal antibody, R33, and the monoclonal antibody A-I-1 (epitope between amino acids 27–48) were most effective and reduced PLTP binding by 70%. These results show that PLTP binds to both apoA-I and apoA-II, and that the PLTP binding domain of apoA-I resides in the amino terminal region.—Pussinen, P. J., M. Jauhiainen, J. Metso, L. E. Pyle, Y. L. Marcel, N. H. Fidge, and C. Ehnholm. Binding of phospholipid transfer protein (PLTP) to apolipoproteins A-I and A-II: location of a PLTP binding domain in the amino terminal region of apoA-I. J. Lipid Res. 1998. 39: 152–161.
Highlights
The interaction of plasma phospholipid transfer protein (PLTP) with High density lipoproteins (HDL) has not been characterized in detail, we have reported that the apoA-I/apoA-II molar ratio in the HDL particle influences PLTP-mediated HDL conversion, but not phospholipid transfer
Because the apoA-I/apoA-II molar ratio in the HDL particle seems to have an important influence on the regulation of PLTP-mediated HDL conversion, the aim of the present study was to analyze the interaction of PLTP with these two major apolipoproteins of human HDL
The interaction of PLTP with lipid-free apoA-I or apoA-II was studied by the ELISA method
Summary
The interaction of plasma phospholipid transfer protein (PLTP) with HDL has not been characterized in detail, we have reported that the apoA-I/apoA-II molar ratio in the HDL particle influences PLTP-mediated HDL conversion, but not phospholipid transfer. Binding of phospholipid transfer protein (PLTP) to apolipoproteins A-I and A-II: location of a PLTP binding domain in the amino terminal region of apoA-I. There is in vitro evidence that plasma phospholipid transfer protein (PLTP) participates in this transport process by remodelling HDL particles and by regenerating primary cholesterol acceptors [2,3,4]. This in vitro data is supported by studies in transgenic mice expressing human PLTP and apoA-I [5], in which the concentration of pre-HDL particles in plasma was elevated dramatically. The presence of apoA-I appears essential for PLTP-mediated HDL conversion and fusion, as it was found that apoA-I-containing particles, but not particles containing only apoA-II were converted by PLTP [12, 13]
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