The 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, a ~20-residue N-terminal fusion peptide domain in the envelope protein binds to target cell membranes and plays a key role in fusion between the viral and cellular membranes during infection. The chemically synthesized HIV fusion peptide or “HFP” catalyzes fusion between membrane vesicles and is a useful model system to understand some aspects of HIV fusion. Previous studies have shown a common trimeric state for envelope protein from several different viruses including HIV and in this study, practical high-yield syntheses are reported for HFP monomer (HFPmn) and chemically cross-linked HFP dimer (HFPdm), trimer (HFPtr), and tetramer (HFPte). The vesicle fusion rates per strand were ordered HFPmn < HFPdm < HFPtr ≈ HFPte and suggested that HFPtr is the smallest catalytically efficient oligomer. Solid-state NMR measurements of ¹³CO chemical shifts were carried out in constructs labeled at either Ala-6 or Ala-15. For all constructs associated with cholesterol-containing membranes, the chemical shifts of both residues correlated with β strand conformation while association with membranes without cholesterol resulted in a mixture of helical and β strand conformations. The dependence of fusion rate on oligomer size is independent of membrane cholesterol content, so one interpretation of the data is fusion activity of both helical and β strand conformations. Membrane location may be a determinant of fusion activity and for all constructs in both conformations, a large fraction of the Ala-15 ¹³COs were 5–6 Å from the ³¹Ps in the lipid headgroups, while the Ala-6 ¹³COs were more distant.