Deuterium NMR studies of the effect of pulmonary surfactant SP-C on the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine headgroup: A model for transbilayer peptides in surfactant and biological membranes

Abstract

Surfactant protein C (SP-C) was isolated from solvent extracts of porcine pulmonary surfactant by gel filtration chromatography. The surfactant protein was combined with dipalmitoylphosphatidylcholine deuterated at the alpha and beta positions of the choline headgroup (DPPC-d4) Deuterium nuclear magnetic resonance spectra were collected as a function of temperature for a series of protein concentrations. The splitting of the alpha-deuteron spectrum in the liquid-crystalline phase was insensitive to temperature but decreased with increasing protein concentration. The response of headgroup conformation to protein concentration was consistent with an interaction between the lipid headgroup dipole and the net positive surface charge associated with the protein. The observed effect per charge on the alpha splitting was less than that reported for singly-charged amphiphiles [Scherer, P. G., & Seelig, J. (1989) Biochemistry 28, 7720-7728] but was similar to that obtained using a multipled-charged amphiphilic polypeptide [Roux, M., Neumann, J.-M., Hodges, R. S., Devaux, P. F., & Bloom, M. (1989) Biochemistry 28, 2313-2321]. This comparison suggests that the charges on SP-C are located near the bilayer surface. The possibility that the headgroup response is sensitive to the degree of clustering of surface charge is discussed. The beta-deuteron splitting in the liquid-crystalline phase decreased with increasing temperature but was relatively insensitive to protein concentration, suggesting that the torsion angle about the C alpha-C beta bond might be sensitive to steric interactions between the lipid headgroup and the protein.

Pulmonary surfactant‐associated polypeptide SP‐C in lipid micelles: CD studies of intact SP‐C and NMR secondary structure determination of depalmitoyl‐SP‐C(1–17)

“…4B, the evolutionarily strictly conserved Lys-Arg dipeptide segment in positions 11-12 [39] is suitably located for interacting with the phosphatidyl choline moieties of DPPC. This would also be in agreement with deuterium NMR studies of selectively deuterated DPPC preparations containing variable amounts of SP-C, which provided evidence for direct interactions between the positive charges of SP-C and the lipid headgroups [40]. Furthermore, the palmitoylcysteinyls at positions 5 and 6 are then located near the exterior surface of the DPPC bilayer (Fig.…”

An X-ray diffraction study of alterations in bovine lung surfactant bilayer structures induced by albumin

“…The hydrophobic surfactant protein, SP-B has been shown to have positively charged amphiphatic alpha-helices that can interact strongly with the anionic phosphatidylglycerol (PG) lipid head-groups in model membrane bilayers (Longo et al, 1992). SP-C also has positive charges in its N-terminal region which is associated with the lipid head-groups in bilayers (Morrow et al, 1993). It seems therefore likely that electrostatic interaction will associate BSA with the SP-B and SP-C of the BLES bilayers.…”

Molecular Structures and Interactions of Pulmonary Surfactant Components

“…Fluorescence measurements indicate that SP-C increases rigidity in the phospholipid head group region but disrupts the interior acyl-chain packing of the bilayer (Horowitz et al, 1992) and that the N-terminus is located in the vicinity of the membrane surface (Horowitz et al, 1993). 'H-NMR spectrosocpy showed that the positively charged amino acids in the N-terminal part of porcine SP-C are located close to the phospholipid head group (Morrow et al, 1993b). No experimental information about the orientation in the membrane of the palmitoyl chains is available.…”