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Elsevier, BBA - Biomembranes, 5(1768), p. 1070-1082, 2007

DOI: 10.1016/j.bbamem.2007.01.020



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Structure and conformation of the disulfide bond in dimeric lung surfactant peptides SP-B1-25 and SP-B8-25

Journal article published in 2007 by Nilanjana Biswas, Alan J. Waring, Frans J. Walther ORCID, Richard A. Dluhy
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Raman spectroscopy was used to determine the conformation of the disulfide linkage between cysteine residues in the homodimeric construct of the N-terminal alpha helical domain of surfactant protein B (dSP-B1-25). The conformation of the disulfide bond between cysteine residues in position 8 of the homodimer of dSP-B1-25 was compared with that of a truncated homodimer (dSP-B8-25) of the peptide having a disulfide linkage at the same position in the alpha helix. Temperature-dependent Raman spectra of the S-S stretching region centered at ∼ 500 cm− 1 indicated a stable, although highly strained disulfide conformation with a χ(CS-SC) dihedral angle of ± 10° for the dSP-B1-25 dimer. In contrast, the truncated dimer dSP-B8-25 exhibited a series of disulfide conformations with the χ(CS-SC) dihedral angle taking on values of either ± 30° or 85± 20°. For conformations with χ(CS-SC) close to the ± 90° value, the Raman spectra of the 8-25 truncated dimers exhibited χ(SS-CC) dihedral angles of 90/180° and 20-30°. In the presence of a lipid mixture, both constructs showed a ν(S-S) band at ∼ 488 cm− 1, corresponding to a χ(CS-SC) dihedral angle of ± 10°. Polarized infrared spectroscopy was also used to determine the orientation of the helix and β-sheet portion of both synthetic peptides. These calculations indicated that the helix was oriented primarily in the plane of the surface, at an angle of ∼ 60-70° to the surface normal, while the β structure had ∼ 40° tilt. This orientation direction did not change in the presence of a lipid mixture or with temperature. These observations suggest that: (i) the conformational flexibility of the disulfide linkage is dependent on the amino acid residues that flank the cysteine disulfide bond, and (ii) in both constructs, the presence of a lipid matrix locks the disulfide bond into a preferred conformation.