Decreased binding of apoA-I to phosphatidylcholine monolayers containing 22:6 n-3 in the sn-2 position.

Previous studies have shown that dietary fish oil can modify the distribution and fatty acyl composition of plasma phospholipids. Although it is known that the type of phos- pholipid can affect the binding of apolipoprotein A-I (apoA-I), little is known about the effect of n-3 fatty acid enrichment in phospholipids on apoA-I binding. We hypothesize that phos- phatidylcholine (PC) surfaces containing n-3 fatty acids at the sn-2 position bind apoA-I less avidly than those containing sn-2 18:l. PC species containing sn-1 16:O and sn-2 18:l (POPC), sn-2 20:5 n-3 (PEPC), or sn-2 22:6 n-3 (PDPC) were used in apoA-I monolayer binding studies. The molecular surface area at any given surface pressure (r) was ordered: PDPC > PEPC > POPC and at u = 2.5 mN/m the molecular surface areas were 86.2, 78.8 and 72 A 2/molecule, respectively. Binding of ( '*C)apoA-I (radiolabeled by reductive methylation) to PDPC at ri = 15 mN/m was less than that for POPC whether expressed as nmol A-I/m2 surface or molecules A-I/1000 PC. The apparent Kd for steady state apoA-I binding to PEPC (2.1 nM) and PDPC (2.2 nM) was greater than that for POPC (1.2 nM); the maximum binding capacity (nmol/m*) was ordered PEPC (9.4) > POPC (8.1)>PDPC (6.7). Similar results were found when a fixed amount of apoA-I was injected beneath the PC monolayers equilibrated at different initial surface pressures. The calculated syrface area available for bound apoA-I was 15, 17, and 23 A'Vamino acid for POPC, PEPC, and PDPC at Iri = 15 mN/m, respectively. We conclude that the binding affinity of apoA-I for PDPC and PEPC is less than that for POPC and that apoA-I bound to PDPC is more loosely folded than that to POPC. These studies suggest that the type of sn-2 fatty acid can influence apoA-I binding to PC.-Parks, J. S., and T. Y. Thuren. Decreased binding of apoA-I to phosphatidylcholine monolayers containing 22:6 n-3 in the sn-2 position. J. Lipid Res. 1993. 34: 779-788.