High density lipoprotein conversion mediated by human plasma phospholipid transfer protein.

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.

mentioning

confidence: 99%

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

Pussinen

Jauhiainen

Metso

et al. 1998

“…In addition, PLTP modulates the size of HDL particles. In this process, termed HDL conversion, human HDL is converted to novel populations of larger particles and smaller pre-␤ -type HDL (5,(13)(14)(15). Although PLTP was already isolated from plasma in the 1980s (16,17), even today little is known of the basic structure-function relationships involved in its activities.…”

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confidence: 99%

Biosynthesis and secretion of human plasma phospholipid transfer protein

Huuskonen

Jauhiainen

Ehnholm

et al. 1998

Plasma phospholipid transfer protein (PLTP) plays a critical role in lipoprotein metabolism and reverse cholesterol transport. We have studied the biosynthesis and secretion of PLTP using a stably transfected inducible HeLa cell line. Pulse-chase analysis revealed that: i ) the major secreted forms of PLTP carry complex N-glycans; ii ) Nglycosylation is crucial for PLTP secretion; iii ) Endo Hresistant forms of PLTP could not be enriched using a 20 Њ C temperature block, indicating that the transport of PLTP from the endoplasmic reticulum to the Golgi apparatus is exceptionally sensitive to low temperatures; and iv ) treatment of the PLTP-producing cells with the reducing agent dithiothreitol caused a reversible secretion arrest, suggesting a role of disulfide bonds in the correct folding of PLTP. Transient expression of C-terminally truncated PLTP variants in COS cells demonstrated that: i ) the 30 C-terminal amino acids are dispensable for PLTP secretion, whereas deletion of 35-50 residues results in a complete absence of secretion; and ii ) the deletion of 30 C-terminal amino acid residues almost completely abolished the phospholipid transfer activity of PLTP. The present study describes for the first time the biosynthesis of phospholipid transfer protein and provides tools for detailed elucidation of the structure-function relationships in the protein.-Huuskonen, J., M. Jauhiainen, C. Ehnholm, and V. M. Olkkonen. Biosynthesis and secretion of human plasma phospholipid transfer protein.

“…Plasma PLTP is susceptible to participate to a number of biological processes by facilitating the transfer of various molecular species, including phospholipids (24,25), lipopolysaccharides (26), ␣-tocopherol (27), and unesterified cholesterol (28) among various lipoprotein classes, as well as between lipoproteins and cells. In addition, PLTP has been shown to promote the simultaneous formation of large-sized HDL and pre-␤ HDL through an HDL fusion process (29)(30)(31)(32). To date, the mechanism of interaction of PLTP with lipoproteins has not been elucidated, and the main determinants of PLTP activity remain to be identified.…”

Section: Discussionmentioning

confidence: 99%

Influence of the electrostatic charge of lipoprotein particles on the activity of the human plasma phospholipid transfer protein

Desrumaux

Athias

Masson

et al. 1998

The aim of the present study was to determine the effect of the electrostatic charge of lipoproteins on the phospholipid transfer activity of the plasma phospholipid transfer protein (PLTP). Progressive decreases in the PLTP-mediated phospholipid transfer rates were observed when the surface potential of isolated high density lipoproteins (HDL) was either reduced from Ϫ 11.7 mV down to Ϫ 15.7 mV by succinylation of apolipoprotein lysyl residues, or increased from Ϫ 11.6 mV up to Ϫ 10.9 mV by replacing apolipoprotein (apo) A-I by apoA-II. When succinylated low density lipoprotein (LDL) series with surface potentials ranging between Ϫ 4.3 mV and Ϫ 14.3 mV were used, successive increase and decrease in phospholipid transfer rates were observed along the electronegativity scale. When various plasma HDL subfractions with surface potentials ranging from Ϫ 10.5 mV to Ϫ 12.5 mV were separated by anion exchange chromatography, PLTPmediated phospholipid transfer activity increased progressively with HDL electronegativity until maximal lipid transfer rates were reached for a mean HDL surface potential of Ϫ 11.6 mV. As the electronegativity of plasma HDL subfractions kept increasing beyond the optimal value, a progressive decrease in PLTP activity was observed. Striking parallelism between cholesteryl ester transfer protein (CETP) and PLTP transfer activity curves obtained with each HDL series were noted, and the optimal HDL surface potential values were remarkably similar, approximating Ϫ 11.6 mV in all the experiments. With isolated plasma LDL subfractions with surface potentials ranging from Ϫ 3.5 mV to Ϫ 5.0 mV, a linear rise in PLTP activity was observed.In conclusion, data of the present study indicate that, like CETP, the activity of PLTP is influenced by electrostatic interactions with lipoproteins.-Desrumaux, C., A. Athias, D. Masson, P. Gambert, C. Lallemant, and L. Lagrost. Influence of the electrostatic charge of lipoprotein particles on the activity of the human plasma phospholipid transfer protein.