title: Structure and conformation of the disulfide bond in dimeric lung surfactant peptides SP-B1-25 and SP-B8-25.
abstract: 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-B(1-25)). The conformation of the disulfide bond between cysteine residues in position 8 of the homodimer of dSP-B(1-25) was compared with that of a truncated homodimer (dSP-B(8-25)) 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 approximately 500 cm(-1) indicated a stable, although highly strained disulfide conformation with a chi(CS-SC) dihedral angle of +/-10 degrees for the dSP-B(1-25) dimer. In contrast, the truncated dimer dSP-B(8-25) exhibited a series of disulfide conformations with the chi(CS-SC) dihedral angle taking on values of either +/-30 degrees or 85+/-20 degrees . For conformations with chi(CS-SC) close to the +/-90 degrees value, the Raman spectra of the 8-25 truncated dimers exhibited chi(SS-CC) dihedral angles of 90/180 degrees and 20-30 degrees . In the presence of a lipid mixture, both constructs showed a nu(S-S) band at approximately 488 cm(-1), corresponding to a chi(CS-SC) dihedral angle of +/-10 degrees . Polarized infrared spectroscopy was also used to determine the orientation of the helix and beta-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 approximately 60-70 degrees to the surface normal, while the beta structure had approximately 40 degrees 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.
authors.affiliation: Department of Chemistry, University of Georgia, Athens, GA 30602-2556, USA.
authors.forename: Nilanjana
authors.initials: N
authors.lastname: Biswas
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Waring
authors.forename: Frans J
authors.initials: FJ
authors.lastname: Walther
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dluhy
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D002942:Circular Dichroism; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry*; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D010715:Phosphatidylglycerols / Q000737:chemistry; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D004220:Disulfides; D010455:Peptides; D010715:Phosphatidylglycerols; D037701:Pulmonary Surfactant-Associated Protein B; D015060:1,2-Dipalmitoylphosphatidylcholine; C051388:1,2-dioleoyl-sn-glycero-3-phosphoglycerol