Conformational mapping of the N-terminal peptide of HIV-1 gp41 in lipid detergent and aqueous environments using 13C-enhanced Fourier transform infrared spectroscopy

doi:10.1110/ps.03407704

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Conformational mapping of the N-terminal peptide of HIV-1 gp41 in lipid detergent and aqueous environments using ¹³C-enhanced Fourier transform infrared spectroscopy

Larry M. Gordon¹, Patrick W. Mobley², William Lee³, Sepehr Eskandari³, Yiannis N. Kaznessis⁴, Mark A. Sherman⁵ and Alan J. Waring¹^,6

¹ Research and Educational Institute (REI) at Harbor-UCLA Medical Center, Torrance, California 90502, USA
² Chemistry Department and
³ Biology Department, California State Polytechnic University, Pomona, California 91768, USA
⁴ Department of Chemical Engineering and Materials Science, and Digital Technology Center, University of Minnesota, Minnesota 55455, USA
⁵ Division of Information Sciences, Beckman Research Institute, City of Hope Medical Center, Duarte, California 91010, USA
⁶ Department of Medicine, UCLA School of Medicine, Los Angeles, California 90095, USA

(RECEIVED September 3, 2003; FINAL REVISION November 26, 2004; ACCEPTED November 28, 2004)

Abstract

The N-terminal domain of HIV-1 glycoprotein 41,000 (gp41) participatesin viral fusion processes. Here, we use physical and computationalmethodologies to examine the secondary structure of a peptidebased on the N terminus (FP; residues 1–23) in aqueousand detergent environments. ¹²C-Fourier transform infrared (FTIR)spectroscopy indicated greater ${alpha}$ -helix for FP in lipid-detergentsodium dodecyl sulfate (SDS) and aqueous phosphate-bufferedsaline (PBS) than in only PBS. ¹²C-FTIR spectra also showeddisordered FP conformations in these two environments, alongwith substantial ${beta}$ -structure for FP alone in PBS. In experimentsthat map conformations to specific residues, isotope-enhancedFTIR spectroscopy was performed using FP peptides labeled with¹³C-carbonyl. ¹³C-FTIR results on FP in SDS at low peptide loadingindicated ${alpha}$ -helix (residues 5 to 16) and disordered conformations(residues 1–4). Because earlier ¹³C-FTIR analysis of FPin lipid bilayers demonstrated ${alpha}$ -helix for residues 1–16at low peptide loading, the FP structure in SDS micelles onlyapproximates that found for FP with membranes. Molecular dynamicssimulations of FP in an explicit SDS micelle indicate that thefraying of the first three to four residues may be due to theFP helix moving to one end of the micelle. In PBS alone, however,electron microscopy of FP showed large fibrils, while ¹³C-FTIRspectra demonstrated antiparallel ${beta}$ -sheet for FP (residues 1–12),analogous to that reported for amyloid peptides. Because FPand amyloid peptides each exhibit plaque formation, ${alpha}$ -helix to ${beta}$ -sheet interconversion, and membrane fusion activity, amyloidand N-terminal gp41 peptides may belong to the same superfamilyof proteins.

Abbreviations: PBS, phosphate-buffered saline • HFIP, hexafluoroiso-propanol • TFE, trifluoroethanol • SDS, sodium dodecyl sulfate • ATR, attenuated-total-reflectance • FTIR, Fourier transform infrared spectroscopy • ¹³C-FTIR, isotopically enhanced ¹³C-Fourier transform infrared spectroscopy • ¹²C-FTIR, conventional FTIR spectroscopy on native peptides • CD, circular dichroism • TEM, transmission electron microscopy • EM, electron microscopy • 2D-NMR, two-dimensional nuclear magnetic resonance • SS ¹³C-NMR, solid-state ¹³C-enhanced nuclear magnetic resonance • ESR, electron spin resonance • POPG, 1-palmitoyl-2-oleoyl phosphatidylglycerol • SP-B_1–25, N-terminal peptide of human surfactant protein B, residues 1–25 • P/L, peptide to lipid molar ratio • LUV, large unilamellar vesicle liposomes • HPLC, high-performance liquid chromatography • Fmoc, 9-Fluorenylmethyloxy-carbonyl • [ ${Theta}$ ]_MRE, mean residue ellipticity (deg cm²/dmole^-1) • TDC, transition dipole coupling • gp41, HIV-1 glycoprotein 41,000 • gp120, HIV-1 glycoprotein 120,000 • HA₂, influenza hemagglutinin protein • IAPP, islet amyloid polypeptide • PrP, prion protein • HB, backbone amide-carbonyl H bonds

Keywords: CD spectroscopy; isotope-enhanced FTIR spectroscopy; computer simulations; electron microscopy; secondary structure; amyloid; prion; fusion

Reprint requests to: Larry M. Gordon, REI at Harbor-UCLA Medical Center, 124 West Carson Street, Bldg. F5 South, Torrance, CA 90502-2064, USA; e-mail: lgordon2{at}san.rr.com; fax: (310) 222-6701.

Supplemental material: See www.proteinscience.org

Article and publication are at http://www.proteinscience.org/cgi/doi/10.1110/ps.03407704.

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