Conformation of apolipoprotein AI in reconstituted lipoprotein particles and particle-membrane interaction. Effect of cholesterol

TRICERRI, M. A.; CORSICO B; TOLEDO, J. D.; GARDA, H. A.; BRENNER, R.R.

BIOCHIMICA AND BIOPHYSICA ACTA

ELSEVIER SCIENCE BV

Año: 1998 vol. 1391 p. 67 - 78

0006-3002

Discoidal recombinant high density lipoproteins rHDL. of apolipoprotein AI apoAI. and palmitoyloleoylphosphatidyl- choline POPC., with or without cholesterol, were prepared by cholate dialysis. By gel filtration, rHDL containing 2?4 Lp2, Lp3 and Lp4. apoAI moleculesrparticle were obtained. The ApoAI conformation in these rHDL was investigated by tryptophan fluorescence, denaturation with guanidine HCl, and immunoreactivity with two monoclonal antibodies recognizing epitopes in the N-terminal and central domains. Data show that apoAI conformation is highly dependent on particle size as well as on cholesterol. The ability of rHDL to interact with lipid bilayer was studied by measuring leakage induction on POPC and POPCrcholesterol vesicles loaded with terbiumrdipicolinic acid. Among the cholesterol-free rHDL, the most efficient ones were the smallest Lp2. Leakage induction on POPC vesicles is dramatically decreased by the presence of cholesterol in Lp2 and Lp3. All the rHDL, but specially those containing cholesterol, induced more leakage on the POPCrcholesterol than on the POPC vesicles. These results suggest that in small cholesterol-poor particles, apoAI could have a conformation determining a high affinity for membranes, which could facilitate cholesterol efflux. After cholesterol enrichment, a conformational change in apoAI could decrease the affinity for membranes allowing the lipoprotein release. q1998 Elsevier Science B.V.