Structure and functions of a dimeric form of surfactant protein SP-C: a Fourier transform infrared and surfactometry study.
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 alpha-helical, beta-sheet, beta-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 beta-sheet structure. In addition, only 10% of the amide (backbone) hydrogens exchanged with deuterium of D2O, indicating that the remaining 90% of amide hydrogens were not accessible to D2O 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.
Baatz
J E
JE
Medical University of South Carolina, Charleston 29425.
Smyth
K L
KL
Whitsett
J A
JA
Baxter
C
C
Absolom
D R
DR
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002417:Cattle; D005583:Fourier Analysis; D066298:In Vitro Techniques; D008567:Membranes, Artificial; D015394:Molecular Structure; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011510:Proteolipids / Q000737:chemistry* / Q000302:isolation & purification / Q000502:physiology; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000302:isolation & purification / Q000502:physiology; D013055:Spectrophotometry, Infrared; D013329:Structure-Activity Relationship; D013499:Surface Properties
D008567:Membranes, Artificial; D011510:Proteolipids; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine