References: Lecithin
J Biol Chem. 1991 Dec 15;266(35):23886-92.
Localization of an apolipoprotein A-I epitope critical for activation of lecithin-cholesterol acyltransferase.
Banka CL, Bonnet DJ, Black AS, Smith RS, Curtiss LK.
Department of Immunology, Research Institute of Scripps Clinic, La Jolla, California 92037.
Apolipoprotein (apo) A-I, the major apoprotein of human high density lipoprotein, is a vital cofactor for lecithin-cholesterol acyltransferase (LCAT), the plasma enzyme responsible for esterification of free cholesterol associated with high density lipoprotein. This esterification is an important component of the reverse cholesterol transport process. An immunochemical approach was used to test the hypothesis that a discrete region of apoA-I was important for LCAT activation. Three human apoA-I-specific monoclonal antibodies were found to inhibit LCAT activation in vitro in a manner directly proportional to their ability to bind to apoA-I-proteoliposomes in fluid phase immunoassays. This relationship was not observed with another four apoA-I-specific antibodies that also were able to bind to the apoA-I proteoliposomes. The use of synthetic peptides representing short amino acid sequences of the apoA-I molecule facilitated the identification of discrete but overlapping apoA-I epitopes for those antibodies that interfered with LCAT-mediated cholesterol esterification. These epitopes spanned amino acid residues 95-121 of mature apoA-I. Therefore, this region is most likely involved in the activation of LCAT by apoA-I.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1721059&dopt=Abstract lecithin
J Struct Biol. 1997 Oct;120(1):1-10.
Hyaluronan-phospholipid interactions.
Pasquali-Ronchetti I, Quaglino D, Mori G, Bacchelli B, Ghosh P.
Biomedical Sciences Department, University of Modena, Italy.
Hyaluronan-phospholipid interactions have been studied in vitro by negative staining and rotary shadowing electron microscopy. Hyaluronan (HA) molecules of different molecular weights (around 170,000; 740,000, and 1.9 x 10(6) Da) were added to phospholipid suspensions (DPPC or egg lecithin) that were in the form of either unilamellar particles or multilamellar vesicles. Suspensions were then gently stirred and incubated at different temperatures from 24 hr up to 7 days. After 24 hr, at temperatures just above the melting point of the phospholipid used, both unilamellar particles and multilamellar vesicles were already shown to change their organization in the presence of HA, giving rise to the formation of (1) huge perforated membrane-like structures lying on the substrate; (2) 12-nm-thick "cylinders" (rollers) with a tendency to aggregate and to form sheets. These structures were seen only in the presence of high-molecular-weight HA, whereas low-molecular-weight HA (170 kDa) induced fragmentation of liposomes and formation of a few short rollers. These data show that phospholipids and HA interact and suggest they may also do so in vivo within the joint cavity, where both chemical species are present, giving rise to complexes which might exhibit peculiar lubricating and protective properties. It is also proposed that such interactions may not be as efficient in arthritic joints, where HA is degraded to low-molecular-weight fragments.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9356287&dopt=Abstract lecithin
Biochemistry. 1995 Oct 17;34(41):13334-42.
Phospholipid binding and lecithin-cholesterol acyltransferase activation properties of apolipoprotein A-I mutants.
Holvoet P, Zhao Z, Vanloo B, Vos R, Deridder E, Dhoest A, Taveirne J, Brouwers E, Demarsin E, Engelborghs Y, et al.
Center for Molecular and Vascular Biology, University of Leuven, Belgium.
Recombinant human apolipoprotein A-I (apo A-I) and three deletion mutants: apo A-I(delta Leu44-Leu126), apo A-I(delta Glu139-Leu170), and apo A-I(delta Ala190-Gln243), purified from the periplasmic space of Escherichia coli, were studied. The rate of turbidity decrease following mixing of apo A-I(delta Ala190-Gln243) with dimyristoylphosphatidylcholine (DMPC) vesicles at 23 degrees C was 10-fold lower than that of the other apo A-I proteins, confirming that the carboxy-terminal region of apo A-I plays a role in rapid lipid binding. The Stokes radii of reconstituted high-density lipoproteins (rHDL), containing dipalmitoylphosphatidylcholine and cholesterol, were larger for the three apo A-I mutants [6.3 nm for apo A-I(delta Leu44-Leu126), 6.1 nm for apo A-I(delta Glu139-Leu170), and 6.5 nm for apo A-I(delta Ala190-Gln243)] than for intact apo A-I (5.0 nm). The mutant rHDL all contained 4 apo A-I molecules per particle as compared to 2 for intact apo A-I. Circular dichroism measurements revealed 8 alpha-helices per apo A-I molecule, 5 per apo A-I(delta Leu44-Leu126), 6 per apo A-I(delta Glu139-Leu170), and 4 per apo A-I(delta Ala190-Gln243) molecule as compared to predicted values of 8, 5, 6, and 6 alpha-helices, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7577918&dopt=Abstract lecithin
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