Structural and Functional Importance of the C-Terminal Part of the Pulmonary Surfactant Polypeptide SP-C

Abstract

A synthetic non-palmitoylated form of the pulmonary surfactant protein SP-C and three peptides of different lengths corresponding to its N-terminal and middle parts were reconstituted into dipalmitoylglycerophosphocholine/phosphatidylglycerol (7:3, by mass) lipid bilayers. The adsorption properties of each reconstituted system were determined by measurement of the surface pressure after injection of the samples underneath an air/water interface. Attenuated total reflection infrared spectroscopy provided information about the structure and orientation of peptides in lipid bilayers. The hydrophobic C-terminal helix is crucial for the rapid adsorption as shortening of the C-terminal part drastically restricted this activity. The C-terminal amino acid sequence can however be replaced with that of the second transmembrane helix of bacteriorhodopsin without significantly modifying the adsorption properties. The data suggest that the hydrophobic C-terminal part allows the anchorage of SP-C in the lipid bilayer in such a manner that the N-terminal domain adopts an optimal conformation and orientation for the rapid adsorption of phospholipids at the air/water interface, and/or that a membrane-spanning helix as such is needed for this activity.

Surfactant protein C peptides with salt-bridges (“ion-locks”) promote high surfactant activities by mimicking theα-helix and membrane topography of the native protein

“…As a further test of this proposition, more detailed 3D information on the structure and membrane topography of SP-C ion-locks will be obtained using 13 C-FTIR spectroscopy (Gordon et al, 2000; Waring et al, 2005), 2D-NMR spectrometry (Sarker et al, 2007) and/or all-atom MD simulation techniques (Walther et al, 2010; Almlen et al, 2010). Additionally, polarized FTIR spectra of SP-C mimics in surfactant lipids should indicate the fatty-acyl chain orientation with respect to the peptide helical axis, and likewise show if there are any protein-induced perturbations in lipid conformations (Clercx et al, 1995). SP-C ion-lock peptides will also be modified to determine whether their surfactant properties may be further optimized.…”

The 21‐residue surfactant peptide (LysLeu4)4Lys(KL4) is a transmembrane α‐helix with a mixed nonpolar/polar surface

“…interface Spreading kinetics of 2% (w/w) of KL4 in a DPPC/PG/PA 68:22:9 (by weight) mixture at an air/water interface was compared to that of native SP-C and SP-C/BR [20], both with transmembranous c~-helices in similar phospholipid mixtures [11,12,14,26]. KL4 is less efficient than native SP-C and SP-C/BR in accelerating the spreading of the lipid mixture and also reaches a lower surface pressure after 1 min (Fig.…”

“…Such interactions are difficult to envision with the KL4 helical surface and orientation in a phospholipid bilayer now found, suggesting another mechanism of action for KL4 in pulmonary phospholipids. The secondary structure and transmembranous orientation of KL4 prompts investigation of its spreading properties in a lipid mixture, since another transmembrane helix (SP-C/BR) with a primary structure which is unrelated to any of the pulmonary surfactant proteins has significant effects on lipid spreading kinetics [20,26]. KL4 does accelerate the spreading of lipids at an air/water interface but it is less effective than both native SP-C and the SP-C/BR hybrid in this respect.…”

Synthetic surfactants with SP‐B and SP‐C analogues to enable worldwide treatment of neonatal respiratory distress syndrome and other lung diseases

“…a). CD, FTIR and NMR spectroscopy of native and depalmitoylated SP‐C and of a synthetic peptides corresponding to the N‐terminal region supported that the α‐helical structure determined in organic solvents exists in lipid detergents and phospholipid bilayers, making it most likely that it represents the structure of SP‐C in native surfactant . Importantly, the length of the entire SP‐C α‐helix determined in organic solvents (37Å), and of its central part that contains exclusively non‐polar residues (23Å), perfectly matches the thickness of a fluid DPPC bilayer and its central part composed of non‐polar fatty acyl chains respectively .…”