PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 9162746

Long-chain polyunsaturated fatty acids in the sn-2 position of phosphatidylcholine decrease the stability of recombinant high density lipoprotein apolipoprotein A-I and the activation energy of the lecithin:cholesterol acyltransferase reaction.

J S Parks·A K Gebre
View original source ↗Export metadata ↓

Abstract

The lecithin:cholesterol acyltransferase (LCAT) kinetics and activation energy and the stability of apolipoprotein A-I (apoA-I) were investigated using recombinant HDL (rHDL) containing phosphatidylcholine (PC), [3H]cholesterol, and apo A-I. The PC component of the rHDL contained sn-1 16:0 and sn-2 18:1 (POPC), 20:4 (PAPC), 20:5 n-3 (PEPC), or 22:6 n-3 (PDPC) or 10% of the respective PC species and 90% sn-1 18:1, sn-2 16:0 PC ether (OPPC ether). The appVmax of the rHDL containing 100% PC varied 10-fold and was ordered POPC > PEPC > PAPC > PDPC, whereas the appKm values varied 19-43 microns PC. The ether-containing rHDL had appVmax values 17-40% of their respective 100% PC rHDL, but maintained the same rank order. The activation energy of LCAT was lower for rHDL containing long chain polyunsaturated fatty acids (PUFA) compared to rHDL containing 100% POPC or 10% PC/90% OPPC ether. The concentration of guanidine HCl (D1/2) required to denature one-half of the apoA-I on rHDL containing long chain PUFA was reduced (1.2-16 M) compared to those containing 100% POPC or 10% PC/90% OPPC (2.2-2.4 M) and there was a strong correlation (r = 0.71) between LCAT activation energy and the stability of apoA-I (i.e., D1/2). We conclude that long chain PUFA in the sn-2 position of PC decreases the catalytic efficiency of LCAT, the activation energy of the LCAT reaction and the stability of apoA-I on the rHDL particles. The strong association between rHDL apoA-I stability and LCAT activation energy suggests that the temperature-dependent step of the LCAT reaction may be sensitive to the strength of the interaction of apoA-I with rHDL PC.

Explore related subjects

Apolipoprotein A-ICholesterol EstersCircular DichroismDose-Response Relationship, DrugFatty Acids, UnsaturatedGuanidinesHumansKineticsLipoproteins, HDLOsmolar ConcentrationPhosphatidylcholine-Sterol O-AcyltransferasePhosphatidylcholinesProtein DenaturationRecombinant ProteinsJournal ArticleResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

J S Parks, A K Gebre. 1997. Long-chain polyunsaturated fatty acids in the sn-2 position of phosphatidylcholine decrease the stability of recombinant high density lipoprotein apolipoprotein A-I and the activation energy of the lecithin:cholesterol acyltransferase reaction.. https://pubmed.ncbi.nlm.nih.gov/9162746/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1998

Studies of synthetic peptides of human apolipoprotein A-I containing tandem amphipathic alpha-helixes.

In mature human apolipoprotein A-I (apo A-I), the amino acid residues 1-43 are encoded by exon 3, whereas residues 44-243 are encoded by exon 4 of the apo A-I gene. The region encoded by exon 4 of the apo A-I gene contains 10 tandem amphipathic alpha-helixes; their location and the class to which they belong are as follows: helix 1 (44-65, class A1), helix 2 (66-87, class A1), helix 3 (88-98, class Y), helix 4 (99-120, class Y), helix 5 (121-142, class A1), helix 6 (143-164, class A1), helix 7 (165-186, class A1), helix 8 (187-208, class A1), helix 9 (209-219, class Y), and helix 10 (220-241, class Y). To examine the effects of multiple tandem amphipathic helixes compared to individual helixes of apo A-I on lipid association, we have studied lipid-associating properties of the following peptides: Ac-44-87-NH2 (peptide 1-2), Ac-66-98-NH2 (peptide 2-3), Ac-66-120-NH2 (peptide 2-3-4), Ac-88-120-NH2 (peptide 3-4), Ac-99-142-NH2 (peptide 4-5), Ac-121-164-NH2 (peptide 5-6), Ac-143-186-NH2 (peptide 6-7), Ac-165-208-NH2 (peptide 7-8), Ac-187-219-NH2 (peptide 8-9), and Ac-209-241-NH2 (peptide 9-10). To study lipid-associating properties of the region encoded by exon 3 of the apo A-I gene, 1-33-NH2 (peptide G) has also been studied. The results of the present study indicate that, among the peptides studied, peptides 1-2 and 9-10 possess significantly higher lipid affinity than the other peptides, with peptide 9-10 having higher lipid affinity than peptide 1-2, as evidenced by (i) higher helical content in the presence of 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), (ii) faster rate of association with DMPC multilamellar vesicles (MLV), (iii) greater reduction in the enthalpy of gel to liquid-crystalline phase transition of DMPC MLV, (iv) higher exclusion pressure from an egg yolk phosphatidylcholine monolayer, and (v) higher partitioning into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine MLV. A comparison of the free energies of lipid association (DeltaG) of the peptides studied here with those studied previously by us [Palgunachari, M. N. , et al. (1996) Arterioscler. Thromb. Vasc. Biol. 16, 328-338] indicates that, except for the peptides 4-5 and 5-6, other peptides possess higher lipid affinities compared to constituent helixes. However, the lipid affinities of the peptides studied here are neither higher than nor equal to the sum of the lipid affinities of the constituent helixes. This indicates the absence of cooperativity among the adjacent amphipathic helical domains of apo A-I for lipid association. As indicated by DeltaG, the lipid affinity of peptide 4-5 is higher than peptide 5 but lower than peptide 4; the lipid affinity of peptide 5-6 is lower than both peptides 5 and 6. Implications of these results for the structure and function of apo A-I are discussed.

Apolipoprotein A-I↗
PubMed1998

Enhanced cholesterol efflux by tyrosyl radical-oxidized high density lipoprotein is mediated by apolipoprotein AI-AII heterodimers.

Myeloperoxidase secreted by phagocytes in the artery wall may be a catalyst for lipoprotein oxidation. High density lipoprotein (HDL) oxidized by peroxidase-generated tyrosyl radical has a markedly enhanced ability to deplete cultured cells of cholesterol. We have investigated the structural modifications in tyrosylated HDL responsible for this effect. Spherical reconstituted HDL (rHDL) containing the whole apolipoprotein (apo) fraction of tyrosylated HDL reproduced the ability of intact tyrosylated HDL to enhance cholesterol efflux from cholesterol-loaded human fibroblasts when reconstituted with the whole lipid fraction of either HDL or tyrosylated HDL. Free apoAI or apoAII showed no increased capacity to induce cholesterol efflux from cholesterol-loaded fibroblasts following oxidation by tyrosyl radical, either in their lipid-free forms or in rHDL. The product of oxidation of a mixture of apoAI and apoAII (1:1 molar ratio) by tyrosyl radical, however, reproduced the enhanced ability of tyrosylated HDL to induce cholesterol efflux when reconstituted with the whole lipid fraction of HDL. HDL containing only apoAI or apoAII showed no enhanced ability to promote cholesterol efflux following oxidation by tyrosyl radical, whereas HDL containing both apoAI and apoAII did. rHDL containing apoAI-apoAIImonomer and apoAI-(apoAII)2 heterodimers showed a markedly increased ability to prevent the accumulation of LDL-derived cholesterol mass by sterol-depleted fibroblasts compared with other apolipoprotein species of tyrosylated HDL. These results indicate a novel product of HDL oxidation, apoAI-apoAII heterodimers, with a markedly enhanced capacity to deplete cells of the regulatory pool of free cholesterol and total cholesterol mass. The recent observation of tyrosyl radical-oxidized LDL in vivo suggests that a similar modification of HDL would significantly enhance its ability to deplete peripheral cells of cholesterol in the first step of reverse cholesterol transport.

Apolipoprotein A-I↗