Conformational mapping of the N-terminal segment of surfactant protein B in lipid using 13C-enhanced fourier transform infrared spectroscopy

L. M. Gordon, K. Y.C. Lee, M. M. Lipp, J. A. Zasadzinski, F. J. Walther, M. A. Sherman, A. J. Waring

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72 Scopus citations

Abstract

Synthetic peptides based on the N-terminal domain of human surfactant protein B (SP-B1-25; 25 amino acid residues; NH2- FPIPLPYCWLCRALIKRIQAMIPKG) retain important lung activities of the full- length, 79-residue protein. Here, we used physical techniques to examine the secondary conformation of SP-B1-25 in aqueous, lipid and structure- promoting environments. Circular dichroism and conventional, 12C-Fourier transform infrared (FTIR) spectroscopy each indicated a predominate α- helical conformation for SP-B1-25 in phosphate-buffered saline, liposomes of 1-palmitoyl-2-oleoyl phosphatidylglycerol and the structure-promoting solvent hexafluoroisopropanol; FTIR spectra also showed significant β- and random conformations for peptide in these three environments. In further experiments designed to map secondary structure to specific residues, isotope-enhanced FTIR spectroscopy was performed with 1-palmitoyl-2-oleoyl phosphatidylglycerol liposomes and a suite of SP-B1-25 peptides labeled with 13C-carbonyl groups at either single or multiple sites. Combining these 13C-enhanced FTIR results with energy minimizations and molecular simulations indicated the following model for SP-B1-25 in 1-palmitoyl-2- oleoyl phosphatidylglyceroh β-sheet (residues 1-6), α-helix (residues 8-22) and random (residues 23-25) conformations. Analogous structural motifs are observed in the corresponding homologous N-terminal regions of several proteins that also share the 'saposin-like' (i.e. 5-helix bundle) folding pattern of full-length, human SP-B. In future studies, 13C-enhanced FTIR spectroscopy and energy minimizations may be of general use in defining backbone conformations at amino acid resolution, particularly for peptides or proteins in membrane environments.

Original languageEnglish (US)
Pages (from-to)330-347
Number of pages18
JournalJournal of Peptide Research
Volume55
Issue number4
DOIs
StatePublished - 2000

Keywords

  • CD spectroscopy
  • Isotope-enhanced FTIR spectroscopy
  • Lung surfactant protein
  • Peptide
  • Saposin
  • Secondary structure

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