Conformation and molecular topography of the N‐terminal segment of surfactant protein B in structure‐promoting environments

Abstract

Although the effects of surfactant protein B (SP-B) on lipid surface activity in vitro and in vivo are well known, the relationship between molecular structure and function is still not fully understood. To further characterize protein structure-activity correlations, we have used physical techniques to study conformation, orientation, and molecular topography of N-terminal SP-B peptides in lipids and structure-promoting environments. Fourier transform infrared (FTIR) and CD measurements of SP-B1_25 (residues 1-25) in methanol, SDS micelles, egg yolk lecithin (EYL) liposomes, and surfactant lipids indicate the peptide has a dominant helical content, with minor turn and disordered components. Polarized FTIR studies of SP-B,-25 indicate the long molecular axis lies at an oblique angle to the surface of lipid films. Truncated peptides were similarly examined to assign more accurately the discrete conformations within the SP-B,_,, sequence. Residues Cys-8-Gly-25 are largely a-helix in methanol, whereas the N-terminal segment Phe-1-Cys-8 had turn and helical propensities. Addition of SP-Bl-25 spin-labeled at the N-terminal Phe (i.e., SP-BT_25) to SDS, EYL, or surfactant lipids yielded electron spin resonance spectra that reflect peptide bound to lipids, but retaining considerable mobility. The absence of characteristic radical broadening indicates that SP-B1-25 is minimally aggregated when it interacts with these lipids. Further, the high polarity of SP-BI-25 argues that the reporter on Phe-1 resides in the headgroup of the lipid dispersions. The blue-shift in the endogenous fluorescence of Trp-9 near the N-terminus of SP-B1-25 suggests that this residue also lies near the lipid headgroup. A summary model based on the above physical experiments is presented for SP-BI-2S interacting with lipids.

Multilayer Formation upon Compression of Surfactant Monolayers Depends on Protein Concentration as Well as Lipid Composition

“…The structure and surface activity of these peptides have been investigated thoroughly both in vitro and in vivo. The conformation of mSP-B-(1-25) was found to be ␣-helical (21,22). In vitro comparison of the surface activity of mSP-B- with that of dSP-B-(1-25) in a captive bubble surfactometer revealed that both peptides reduced the surface tension, with the dimeric peptide expressing better ability to lower surface tension than the monomeric peptide (23).…”

Comparison of functional efficacy of surfactant protein B analogues in lavaged rats

“…The SP-C 1±35 peptide was based on the human SP-C sequence and palmitoylated as reported previously [20,22]. The present study group has described conformation of the structure of these peptides [21,22].…”

Synthetic Surfactant Protein Analogues

“…Peptides covering different parts of the native molecule have been synthesized and evaluated in vitro and in vivo. Peptides covering the C-terminal part and containing at least 17 amino acids accelerate surfactant spreading and improve static lung compliance in fetal rabbits [16,17] and synthetic replicas of the N-terminal part of the polypeptide chain, in particular positions 1-25, mimic most of the activities performed by native, full length SP-B [18][19][20]. Extrapolation to physiological conditions from the latter studies is difficult since Synthetic Surfactant Protein Analogues Biol Neonate 1998;74(suppl 1):9-14 13 in many experiments PA was the only lipid present, while the amount of PA in surfactant is low.…”