HIV Fusion Peptide and Its Cross-Linked Oligomers: Efficient Syntheses, Significance of the Trimer in Fusion Activity, Correlation of β Strand Conformation with Membrane Cholesterol, and Proximity to Lipid Headgroups

摘要

For enveloped viruses such as HIV, an ∼20-residue N-terminal fusion peptide domain in thenenvelope protein binds to target cell membranes and plays a key role in fusion between the viral andncellular membranes during infection. The chemically synthesized HIV fusion peptide (HFP) catalyzesnfusion between membrane vesicles and is a useful model system for understanding some aspects of HIVnfusion. Previous studies have shown a common trimeric state for the envelope protein from several differentnviruses, including HIV, and in this study, practical high-yield syntheses are reported for HFP monomern(HFPmn) and chemically cross-linked HFP dimer (HFPdm), trimer (HFPtr), and tetramer (HFPte). Thenvesicle fusion rates per strand were ordered as follows: HFPmn HFPdm HFPtr ≈ HFPte. Thisnsuggested that HFPtr is the smallest catalytically efficient oligomer. Solid-state NMR measurements ofn13nCO chemical shifts were carried out in constructs labeled at either Ala-6 or Ala-15. For all constructsnassociated with cholesterol-containing membranes, the chemical shifts of both residues correlated with u0001nstrand conformation while association with membranes without cholesterol resulted in a mixture of helicalnand u0001 strand conformations. The dependence of fusion rate on oligomer size is independent of membranencholesterol content, so one interpretation of the data is fusion activity of both helical and u0001 strandnconformations. Membrane location may be a determinant of fusion activity, and for all constructs in bothnconformations, a large fraction of the Ala-15 13nCO groups were 5 6 Å from the 31nP atoms in the lipidnheadgroups, while the Ala-6 13nCO groups were more distant