Synthetic viruslike particles and hybrid constructs based on lipopeptide self-assembly

The spontaneous self-assembly of biological molecules to form viruslike particles (VLPs) represents a key area of research in biotechnology and pharmacology.^[1] Use of VLP-based vaccines is expected to contribute significantly to new advances in health care; for example, the human papilloma virus (HPV)^[2] and hepatitis B virus^[3] vaccines were recently approved by the Food and Drug Administration (FDA). VLPs are most commonly derived from recombinant proteins that assemble to form capsids devoid of native nucleic acids. Significantly, the oligomeric nature of the VLP structure facilitates the display of multiple copies of a bound antigen, and as a consequence elicits a vigorous immune response when introduced to the body. Recently, synthetic VLPs (SVLPs) that require no cell-culturing or recombinant DNA methods for production have been produced using artificial building blocks.^[4] In particular, a persistent micellelike nanostructure with VLP properties was recently prepared using a synthetic lipopeptide (FB-6) comprising a primary sequence of 50 amino acids derived from thea-helical-forming heptad repeat region 1 (Ala 153 - Gln 202) of the F1 glycoprotein of respiratory syncytial virus (RSV)^[5] with two additional Gly residues at the N-terminus. The peptide was coupled at the N terminus via a succinate linker to 1, 3-dipalmitoyl-glycero-2- phosphoethanolamine to produce an amphiphilic lipopeptide consisting of an α-helical peptide headgroup and phospholipid tail (Supporting Information, Figure S1a). Circular-dichroism studies indicated that the lipopeptide was self-associated into trimeric coiled-coil subunits comprising a parallel triple-helix bundle and six fatty acid chains, which subsequently self-assembled in water to produce a structurally persistent micelle (Supporting Information, Figure S1b). Transmission electron microscopy (TEM) and analytical ultracentrifugation studies indicated, respectively, that the micelles were 20±5 nm in diameter and consisted of approximately 72 lipopeptide molecules (24 triplehelix bundles).^[4] By coupling synthetic antigens to the lipoprotein C-terminus prior to self-assembly, an analogous nanostructure with viruslike properties was produced.