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

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Abstract

Surfactant proteins SP-B (Mr = 8700, reduced) and SP-C (Mr = 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 (Mr = 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 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.

References (26)

  • S.-H. Yu et al.

    Biochim. Biophys. Acta

    (1990)
  • A.D. Horowitz et al.

    Biochim. Biophys. Acta

    (1992)
  • G.F. Ross et al.

    J. Biol. Chem.

    (1986)
  • J.E. Baatz et al.

    Chem. Phys. Lipids

    (1991)
  • R.W. Olafson et al.

    Biochem. Biophys. Res. Commun.

    (1987)
  • J. Johansson et al.

    FEBS Lett.

    (1988)
  • T.N. Earnest et al.

    Biophys. J.

    (1990)
  • M.D. Bazzi et al.

    Biophys. J.

    (1985)
  • E. Nabedryk et al.

    Biophys. J.

    (1988)
  • G.I. King et al.

    Biophys. J.

    (1986)
  • J. Goerke et al.
  • R.H. Notter et al.

    J. Appl. Physiol.: Respir. Environ. Exerc. Physiol.

    (1984)
  • J.A. Whitsett et al.

    Pediatr. Res.

    (1986)
  • Cited by (0)

    This work was supported in part by an American Lung Association Research Grant (J.E.B.) and the Program of Excellence in Molecular Biology, NIH HL41496 and the Children's Hospital Research Foundation.

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