Pig apolipoprotein AI self-association and interaction with L-alpha-dimyristoylphosphatidylcholine as compared with human apolipoprotein AI

Abstract

Associative properties of apolipoprotein AI of HDL were compared in the pig and human. Self-association of apo AI (determined by dimethylsuberimidate cross-linking) occurred preferentially as tetramers in pig AI as compared to equal proportions of tetra and pentamers in human. Like human apo AI, the pig apoprotein is susceptible of recombining with increasing concentrations of phospholipids (dimyristoylphosphatidylcholine). Both apoproteins first give rise to particles containing 2 AI molecules (DMPC : AI molar ratio of 20 - 200) then to larger particles containing 3 apoprotein molecules (DMPC : AI molar ratio of 200 - 600). Despite these similarities in phospholipid association, pig apolipoprotein displayed less affinity for the lipid vesicles and should, therefore, be more readily exchangeable. Upon incubation with human HDL, however, pig apo AI displaces human apo AI, but it does not associate with it in mixed particles, and forms heavy particles from which the human apoprotein has been totally displaced. Protein-protein associations at the surface of lipoproteins therefore exhibit definite species specificity.