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.

In vivo Raman Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers

“…material). Generally, our Raman assignments correlate with those in the literature [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46]. The Raman spectrum of the SC is dominated by vibrational bands of its structural proteins, lipids, and tissue water.…”

Functional importance of the NH2-terminal insertion sequence of lung surfactant protein B

“…This proposed splayed structure of the helix dimer is supported by Raman and polarized FTIR spectroscopy studies performed on the SP-B 1-25 and SP-B 8 -25 disulfide linked dimer. While the disulfide linkage is strained, it can clearly permit dimer helical splays and surface dependent helix orientation in surfactant lipids, in agreement with our proposed model (6). Additionally, recent work on lung surfactant peptoids, or peptide mimics, showed that the linkage of monomers by a rigid triazole moiety to form a dimer enhanced in vitro surface activity in a lipid film relative to its monomeric counterparts (16).…”

“…While there are no high-resolution crystal or NMR structures of the native SP-B protein, the structure of the NH 2 terminus up to residue 25 is well defined as determined by a combination of NMR, FTIR, and Raman spectroscopy (6,22,38,53,59,71). Residues 1-9 (FPIPLPYCW), proposed to act as an "insertion sequence," comprise a hydrophobic region containing a poly-proline-like sequence.…”

Design of Surfactant Protein B Peptide Mimics Based on the Saposin Fold for Synthetic Lung Surfactants

“…Because prior results with SP-B peptides [17,18,58,63,79,80] suggested that the N-terminal sequence (i.e., residues 1–7) plays key roles in the surfactant properties of full-length SP-B, we next engineered the Super Mini-B (S-MB), a 41-residue peptide mimic in which residues 1–7 was covalently attached to the N-terminus of MB [S-MB (residues 1–41): FPIPLPYCWLCRALIKRIQAMIPKGGRMLPQLVCRLVLRC]. S-MB might be expected to show higher surfactant activity than MB, because the former peptide may more accurately mimic the leaflet structure containing the N- and C-terminal domains of SP-B (Figure 1).…”