Interaction between perdeuterated dimyristoylphosphatidylcholine and low molecular weight pulmonary surfactant protein SP-C

Abstract

A low molecular weight hydrophobic protein was isolated from porcine lung lavage fluid using silicic acid and Sephadex LH-20 chromatography. The protein migrated with an apparent molecular weight of 5000-6000 on SDS-PAGE under reducing and nonreducing conditions. Gels run under reducing conditions also showed a minor band migrating with a molecular weight of 12,000. Amino acid compositional analysis and sequencing data suggest that this protein preparation contains intact surfactant protein SP-C and about 30% of truncated SP-C (N-terminal leucine absent). The surfactant protein was combined with perdeuterated dimyristoylphosphatidylcholine (DMPC-d54) in multilamellar vesicles. The protein enhanced the rate of adsorption of the lipid at air-water interfaces. The ability of the protein to alter normal lipid organization was examined by using high-sensitivity differential scanning calorimetry (DSC) and 2H nuclear magnetic resonance spectroscopy (2H NMR). The calorimetric measurements indicated that the protein caused a decrease in the temperature maximum (Tm) and a broadening of the phase transition. At a protein concentration of 8% (w/w), the enthalpy change of transition was reduced to 4.4 kcal/mol compared to 6.3 kcal/mol determined for the pure lipid. NMR spectral moment studies indicated that protein had no effect on lipid chain order in the liquid-crystal phase but reduced orientational order in the gel phase. Two-phase coexistence in the presence of protein was observed over a small temperature range below the pure lipid transition temperature. Spin-lattice relaxation times (T1) were not substantially affected by the protein. Transverse relaxation time (T2e) studies suggest that the protein influences slow lipid motions.

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)

“…This affords a molecular explanation of the recent finding that SP-C is predominantly monomeric in fluid DPPC/ dipalmitoylphosphatidylglycerol (DPPG) vesicles, but undergoes self-aggregation in the same lipid mixture below the transition temperature between gel phase and liquid-crystalline phase [38]. Accordingly, the decrease of the phase transition temperature of phospholipid vesicles caused by SP-C [10] may be due to peptide aggregates disrupting the lipid packing in the gel phase.…”

“…These 'lamellar bodies' are excreted into the alveolar liquid subphase, where they are converted into more complex bilayer structures ('tubular myelin'), from which the surfaceactive monolayers are eventually formed. SP-C is thought to have an important role in facilitating the conversion of subphase bilayer structures into surface-active DPPC monolayers at the air/liquid interface [5][6][7][8][9][10]. Since large-scale production of natural SP-B and SP-C is difficult, the development of synthetic, possibly non-peptide analogs for therapeutic purposes is of great potential interest [11,12].…”

The proteins of the surfactant system

“…These effects were increased by the simultaneous presence of Ca 2+ and PG. Other biophysical measurements [279], although not conclusive, suggested that SP-C might increase lipid adsorption, by inducing the formation of non-bilayer lipid structures. Using fluorescent phospholipid probes, HOROWITZ et al [280] found that SP-C orders the bilayer surface, but disrupts the interior acyl chain packing.…”

Molecular Structures and Interactions of Pulmonary Surfactant Components

“…In contrast to the nearperfect fit between SP-C and a fluid Pam,GroPCho bilayer, the peptide appears poorly suited to be incorporated into a gel-phase Pam,GroPCho bilayer, with an approximate thickness of 3.9 nm of the hydrocarbon part alone (Zhang et al, 1992), or a phospholipid monolayer, unless it is significantly tilted from a normal to the bilayerlmonolayer plane. Simatos et al (1990) showed by WNMR spectroscopy that SP-C has no effect on lipid chain order in the liquid-crystal phase but reduced orientational order in the gel phase. In gel-phase lipids, the SP-C helix is significantly shorter than the thickness of the lipids and such mismatches promote phase separations of peptides and lipids (Zhang et al, 1992).…”