title: The molecular area characteristics of the HIV-1 gp41-fusion peptide at the air/water interface. Effect of pH.
abstract: The putative fusion peptide of HIV-1 is a highly surface active substance. Relevant measurements with the Langmuir monolayer technique have been carried out for a broad range of the pH in the aqueous subphase. The data are processed towards a quantitative analysis of the partitioning equilibrium between the interfacial and aqueous moieties. Our results reveal a pronounced decrease of the surface area per peptide molecule upon monolayer compression. This phenomenon could be interpreted in terms of an orientational transition experienced by an alpha-helical peptide structure. The area requirements at any fixed lateral pressure pass through a distinct minimum at a pH of 5.5 (+/-0.5). Such an apparent isoelectric point was confirmed by isoelectric focusing of peptide aggregates. Accordingly a drastic drop of the pK-values of the two basic amino acid residues in comparison with an aqueous medium is indicated. It can be readily explained based on an inherent decrease of the effective dielectric constant. The observed low pH in favor of an enhanced surface affinity of the peptide may be a significant factor concerning its function as a fusion promoting agent.
authors.affiliation: Department of Biophysical Chemistry, Biocenter of the University, Basel, Switzerland.
authors.forename: S E
authors.initials: SE
authors.lastname: Taylor
authors.forename: G
authors.initials: G
authors.lastname: Schwarz
mesh_terms: D000595:Amino Acid Sequence; D015700:HIV Envelope Protein gp41 / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000494:pharmacology; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D015700:HIV Envelope Protein gp41; D010446:Peptide Fragments