Structure and functions of a dimeric form of surfactant protein SP-C: a Fourier transform infrared and surfactometry study

• Published in: Chemistry and physics of lipids Vol. 63; no. 1; pp. 91 - 104
• Main Authors: Baatz, John E., Smyth, Kathleen L., Whitsett, Jeffrey A., Baxter, Connie, Absolom, Darryl R.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.11.1992; Elsevier Science
• Subjects: 1,2-Dipalmitoylphosphatidylcholine - chemistry; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Biophysical Phenomena; Biophysics; Cattle; Fourier Analysis; Fourier transform-infrared spectrometry; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Membranes, Artificial; Miscellaneous; Molecular Structure; Protein Conformation; Protein Structure, Secondary; Proteins; Proteolipids - chemistry; Proteolipids - isolation & purification; Proteolipids - physiology; pulmonary surfactant; pulmonary surfactant protein B (SP-B); pulmonary surfactant protein C, monomeric form (SP-C); Pulmonary Surfactants - chemistry; Pulmonary Surfactants - isolation & purification; Pulmonary Surfactants - physiology; secondary structure; Spectrophotometry, Infrared; Structure-Activity Relationship; Surface Properties; EggPG; pulmonary surfactant protein C, monomeric form (SP-C); PmA; FT-IR; [SP-C] 2; secondary structure; pulmonary surfactant protein B (SP-B); SP-B; Fourier transform-infrared spectrometry; SP-C; DMPC; DOPC; pulmonary surfactant; ATR; DPPC; Proteins; Infrared spectrometry; Vertebrata; Fourier transformation; Mammalia; Bovine; Pulmonary surfactant; Surface properties; Dimer; Artiodactyla; Secondary structure; Ungulata
• ISSN: 0009-3084; 1873-2941
• DOI: 10.1016/0009-3084(92)90026-L

Surfactant proteins SP-B ( M r = 8700, reduced) and SP-C ( M r = 3000–6000, major form, non-reduced) interact with surfactant phospholipids to enhance their surface active properties. In the present study, we describe the structural and functional characteristics of a novel dimeric form of bovine SP-C ( M r = 9000, non-reduced), which is identified as [SP-C] 2. Dimeric SP-C exhibits surface tension-lowering properties differing from those of monomeric SP-C and enhances the surface properties of bovine SP-B/phospholipid mixtures. Chemical analysis indicated that [SP-C] 2 was not acylated at the cysteinyl residues. Fourier transform-infrared spectroscopy (FT-IR) was utilized to determine the secondary structures of [SP-C] 2 in DPPC films. Relative percentages of α-helical, β-sheet, β-turn and random coil structures were calculated by peak fit analysis of the amide I band of the FT-IR spectra indicating that, in contrast to the helical structure of monomeric SP-C, [SP-C] 2 exhibits almost exclusively β-sheet structure. In addition, only 10% of the amide (backbone) hydrogens exchanged with deuterium of D 2O, indicating that the remaining 90% of amide hydrogens were not accessible to D 2O due to strong hydrogen bonding or their location in a hydrophobic environment. Dimerization of SP-C effects a major change in secondary structure, a factor which may play a role in the interaction of SP-C with phospholipids in pulmonary surfactant.