Effect of long chain polyunsaturated fatty acids in the sn-2 position of phosphatidylcholine on the interaction with recombinant high density lipoprotein apolipoprotein A-I

Abstract

The effects of polyunsaturated fatty acids (PUFA) on the structure of recombinant high density lipoprotein (rHDL) was investigated using homogeneous particles containing phosphatidylcholine (PC), [ 3 H]cholesterol, and apolipoprotein A-I (apoA-I). The PC component of the rHDL contained sn -1 16:0 and sn -2 18:1 (POPC), 18:2 (PLPC), 20:4 (PAPC), 20:5 n-3 (PEPC), or 22:6 n-3 (PDPC). The concentration of guanidine HCl (D 1/2 ) required to denature one-half of the apoA-I on rHDL containing long chain PUFA was reduced (1.57-1.70 m ) compared to those containing POPC (2.83 m ). Intrinsic apoA-I tryptophan fluorescence emission intensity and lifetimes were decreased for rHDL containing long chain PUFA compared to POPC and PLPC rHDL. Monoclonal antibody binding studies demonstrated that apoA-I had decreased immunoreactivity with monoclonal antibodies spanning amino acid residues 115-147 in rHDL containing long chain PUFA. PC lipid fluidity, measured as diphenylhexatriene (DPH) fluorescence polarization, was increased in PUFA rHDL compared to POPC rHDL. There also was a strong correlation between the number of sn -2 double bonds in rHDL and DPH fluorescence lifetime ( r 2 ‫؍‬ 0.89). LCAT reactivity of the homogeneous size rHDL was ordered POPC ‫؍‬ PLPC Ͼ PAPC Ͼ PEPC Ͼ PDPC. We conclude that rHDL with long chain PUFA in the sn -2 position of PC contain apoA-I that is less stable and in a different conformation than that in POPC rHDL and have a fatty acyl region that is more fluid and hydrated. The weaker interaction of apoA-I with PC containing PUFA may lead to hypercatabolism of apoA-I in plasma explaining, in part, the decreased plasma HDL and apoA-I concentrations seen with PUFA diets.-Huggins, K. W., L. K. Curtiss, A. K. Gebre, and J. S. Parks. Effect of long chain polyunsaturated fatty acids in the sn -2 position of phosphatidylcholine on the interaction with recombinant high density lipoprotein apolipoprotein A-I.

Phosphatidylcholine fluidity and structure affect lecithin:cholesterol acyltransferase activity

“…To our knowledge this is the first report that LCAT activity decreases as double bonds are positioned closer to the methyl terminus of PC sn-2 fatty acyl chains. Our previous studies have shown that n -3 fatty acyl chains in the sn-2 position of PC were less reactive with LCAT than n-6 or n-9 species, but in those studies the fatty acyl chain length and number of double bonds was not controlled (16,20). The effect of sn-2 fatty acyl double bond position on LCAT activity cannot be explained by bulk PC fluidity alone for several reasons.…”

“…In a third experiment, rHDL were made that contained 10% of the PC species containing 18 carbon sn -2 fatty acyl chains (from Study 1) and 90% OPPC ether as described previously (16). Compositional analysis of the rHDL, chemical crosslinking of apoA-I, and gradient gel electrophoresis were performed as described previously (16,19,20).…”

Negative Charge at Amino Acid 149 Is the Molecular Determinant for Substrate Specificity of Lecithin:Cholesterol Acyltransferase for Phosphatidylcholine Containing 20-Carbon sn-2 Fatty Acyl Chains

“…Recombinant His 6tagged LCAT enzyme was eluted from the column with wash buffer containing 50 mM imidazole (Fisher) and 10% glycerol (Fisher) and immediately frozen at -70 °C. Secondary structural analysis of hLCATh6 and hE149Ah6 as performed by circular dichroism spectroscopy was described previously (21). The secondary structural content was estimated with Neural, a network approach using the CDNN software (22).…”

“…LCAT Binding Assay. rHDL were prepared with POPC or PAPC and purified to apparent homogeneity using FPLC as described previously (21). rHDL in PBS were mixed with 10 mg/mL EZ-Link Sulfo LC biotin reagent (Pierce, Rockford, IL) at an apoA-I:biotin reagent mass ratio of 2.7.…”

Dietary n-3 polyunsaturated fat increases the fractional catabolic rate of medium-sized HDL particles in African green monkeys

“…A recent study demonstrated that large HDL compared with small HDL were bound to scavenger receptor BI on the surface of CHO cells with higher affinity, and the authors concluded that HDL size and/or apoA-I conformation influences the binding of HDL subfractions to scavenger receptor BI (52). We have previously shown that recombinant HDL made with phosphatidylcholine containing n-3 fatty acids (docosahexanoic and eicosapentaenoic acid) in the sn-2 position have apoA-I that is in a different conformation and has a decreased stability compared with particles containing phosphatidylcholine with oleic acid in the sn-2 position (53). It is unlikely that a difference in lipid fluidity, per se, will manifest itself exclusively in the medium HDL subfractions, resulting in a selective increase in catabolism.…”