[Show abstract][Hide abstract] ABSTRACT: Two glutamic acid-rich fusion peptide analogs of influenza hemagglutinin were synthesized to study the organization of the charged peptides in the membranous media. Fluorescence and gel electrophoresis experiments suggested a loose association between the monomers in the vesicles. A model was built which showed that a positional difference of 3, 7 and 4, 8 results in the exposure of Glu3 and Glu7 side chains to the apolar lipidic core. Supportive results include: first, pK(a) values of two pH units higher than reference value in aqueous medium for Glu3 and Glu7 CgammaH, whereas the deviation of pK(a) from the reference value for Glu4 and Glu8 CgammaH is substantially smaller; second, Hill coefficients of titration shift of these protons indicate anti-cooperativity for Glu3 and Glu7 side chain protons but less so for Glu4 and Glu8, implying a strong electrostatic interaction between Glu3 and Glu7 possibly resulting from their localization in an apolar environment; third, positive and larger titration shift for NH of Glu3 is observed compared to that of Glu4, suggesting stronger hydrogen bond between the NH and the carboxylic group of Glu3 than that of Glu4, consistent with higher degree of exposure to hydrophobic medium for the side chain of Glu3.
[Show abstract][Hide abstract] ABSTRACT: The structure and membrane interaction of the internal fusion peptide (IFP) fragment of the avian sarcoma and leucosis virus (ASLV) envelope glycoprotein was studied by an array of biophysical methods. The peptide was found to induce lipid mixing of vesicles more strongly than the fusion peptide derived from the N-terminal fusion peptide of influenza virus (HA2-FP). It was observed that the helical structure was enhanced in association with the model membranes, particularly in the N-terminal portion of the peptide. According to the infrared study, the peptide inserted into the membrane in an oblique orientation, but less deeply than the influenza HA2-FP. Analysis of NMR data in sodium dodecyl sulfate micelle suspension revealed that Pro13 of the peptide was located near the micelle-water interface. A type II beta-turn was deduced from NMR data for the peptide in aqueous medium, demonstrating a conformational flexibility of the IFP in analogy to the N-terminal FP such as that of gp41. A loose and multimodal self-assembly was deduced from the rhodamine fluorescence self-quenching experiments for the peptide bound to the membrane bilayer. Oligomerization of the peptide and its variants can also be observed in the electrophoretic experiments, suggesting a property in common with other N-terminal FP of class I fusion proteins.
Preview · Article · Jan 2005 · European Journal of Biochemistry
[Show abstract][Hide abstract] ABSTRACT: Two synthetic mutants of influenza HA2 fusion peptide (residues 1-25), containing Glu on the polar (residues 4,8-E5(4,8)) or the hydrophobic (residues 3,7-E5(3,7)) face of the amphipathic helix, were synthesized and labeled with NBD at the N-terminus. Introduction of Glu residues into the fusion peptide leads to increased sensitivity of various biochemical properties to pH compared to the wild type. The E5 peptides showed a decrease of alpha-helix content and increase of beta-sheet structure. Lipid binding was diminished, but not abolished even at high pH. The E5 analogs penetrate the lipid bilayer less deeply than the wild type, especially at high pH. The N-terminal half of the peptide showed significant variation of the depth of the penetration into the lipid bilayer. Both E5 peptides were fusion active. The properties of E5(3,7) were more affected by the Glu substitution and showed greater variation with pH than E5(4,8).
No preview · Article · Jun 2004 · Archives of Biochemistry and Biophysics
[Show abstract][Hide abstract] ABSTRACT: Mutations of the glycine residue at the amino terminus of HA2 have been shown to have a large effect on the fusion activity of HA2, the extent of which apparently correlates with the side chain bulkiness of the substituting amino acids. To investigate into the cause of abrogation in fusogenicity and virus-promoted fusion mechanism, we synthesized several peptides in which this glycine was substituted by serine, glutamic acid, or lysine. 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl sn-glycero-3-phosphoglycerol (DMPG) were used as model membranes in the fluorescence, circular dichroism (CD), and FTIR measurements while sodium dodecyl sulfate was used in NMR studies. We found that, for the less active variants, affinity to membrane, degree of solvent dehydration, lipid perturbation, depth of insertion, and helicity were less. Comparison of affinity to membrane bilayer among these analogs revealed that binding of the fusion peptide is determined largely by the hydrophobic effect. Additionally, the orientation is closer to the membrane normal for the wild-type fusion peptide in the helix form while the inactive analogs inserted more parallel to the membrane surface.
Full-text · Article · Jun 2003 · Biochimica et Biophysica Acta
[Show abstract][Hide abstract] ABSTRACT: A number of peptides and peptide analogs derived from the membrane proximal region of gp41 ectodomain are found to be effective inhibitors of human immunodeficiency virus type 1 (HIV-1)-mediated fusion events. One of them, T20 (aa 638-673), was found disordered and sparingly soluble in water, but became soluble upon mixing with selected, structured peptides from the amino terminal heptad repeat (HR1) region of gp41 using a simple and sensitive method of reduction in the scattering of T20 suspension. From the results on mapping the locus of interaction with T20 by employing partially overlapping peptides derived from HR1, it was concluded that the LLSGIV segment was a critical docking site for the C-terminal peptide of gp41 in its putative inhibitory action consistent with a previous fluorescence study. It was also found that peptides capable of solubilizing T20 dispersion have a high content of helix, as well as beta-strand, conformation in aqueous solution. Specificity of T20/HR1-derived peptide binding was ascertained by using a scrambled sequence of a T20-active peptide and a plateau in scattering reduction of T20 suspension with variation in the concentration of a T20-active HR1 peptide. Implications on the mechanism of T20 inhibition and the sequence of folding of the gp41 core structure are discussed.
No preview · Article · May 2003 · Protein engineering