BRANCHED SYNTHETIC CONSTRUCTS THAT MIMIC THE PHYSICOCHEMICAL PROPERTIES OF APOLIPOPROTEIN-AI IN RECONSTITUTED HIGH-DENSITY-LIPOPROTEINS

Amphipathic helical repeats are considered as the structural units of numerous apolipoproteins and have been described as being responsible for the interaction of apolipoproteins with phospholipids in high-dens ity lipoproteins (HDL). Furthermore, apolipoproteins, and especially a polipoprotein AI (apoAI), are involved in various biological functions of these circulating particles in plasma. Studies with synthetic pept ides corresponding to domains of the apoAI sequence have however shown that short 39-residue fragments do not interact strongly enough with phospholipids to generate particles that correctly mimic the physico-c hemical properties of HDL reconstituted with native apoAI [Vanloo, B., Demoor, L., Boutillon, C., Lins, L., Baert, J., Fruchart, J. C., Tart ar, A. & Rosseneu, M. (1995) Association of synthetic peptide fragment s of human apolipoprotein A-I with phospholipids, J. Lipid Res, 36, 16 86-1696.]. Here we show that synthetic branched multimeric peptides, o ften used as carriers for the design of synthetic vaccines (multiple-a ntigen peptides), can be used to mimic the physicochemical properties of apoAI in HDL. This type of molecule is obtained by using a small co re matrix of Lys residues bearing radially branched synthetic peptides as dendritic arms. We compared the lipid-binding capacities and the s tructural properties of a linear peptide corresponding to residues 145 -183 of apoAI [apoAI-(145-183)-peptide] with those of two multimeric p eptides consisting respectively of three [trimeric apoAI-(145-183)] an d four copies [tetrameric apoAI-(145-183)] of the selected sequence, b ranched on a covalent core matrix. This paper provides evidence for th e increased abilities of the multimeric peptides to associate with pho spholipids compared with the short linear peptides. Moreover, the trim eric apoAI-(145-183) peptide was most efficient in mimicking the physi co-chemical and structural properties of native apoAI in reconstituted HDL. As tools adequate to unravel the structure/function relationship of separate apolipoprotein domains are still missing, these multimeri c peptides might constitute an alternative approach to linear peptides which are poor mimetics and to protein mutants which are difficult to produce and only provide information about the total sequence.