Effect of acylation on structure and function of surfactant protein C at the air-liquid interface.
Pulmonary surfactant protein C (SP-C) is a small hydrophobic peptide that is palmitoylated on 2 adjacent cysteine residues. SP-C enhances the adsorption of phospholipids into a monolayer. The function of the acylation is not clear yet. The experiments described in this article were carried out in order to investigate the function of SP-C acylation in (protein-catalyzed) lipid monolayer formation, and in bilayer interactions. Palmitoylated and nonpalmitoylated human recombinant SP-C were used. In addition, a nonacylated SP-C with a Cys-->Ser mutations was included in these studies. In Wilhelmy plate experiments using negatively charged, protein-containing phospholipid monolayers and negatively charged vesicles, CaCl2 was required to obtain a maximal insertion rate of lipids into the monolayer. If the negatively charged phospholipids in the monolayer were replaced by neutral phospholipids, CaCl2 was only required to show a maximal SP-C-catalyzed insertion rate (if the molecule is palmitoylated, but not if nonpalmitoylated proteins were added). In pressure area measurements, the palmitoylated protein showed a different change in pressure as a function of the surface area, as compared with the nonpalmitoylated proteins. Circular dichroism experiments showed that all three proteins had a high content of alpha-helix. All three proteins showed a preferential orientation at the air-water interface, but the palmitoylated protein has an orientation which is more parallel to the monolayer than that of the nonpalmitoylated proteins. It is concluded that acylation of SP-C alters structural and physical properties of this protein.
Creuwels
L A
LA
Laboratory of Veterinary Biochemistry, University of Utrecht, The Netherlands.
Demel
R A
RA
van Golde
L M
LM
Benson
B J
BJ
Haagsman
H P
HP
D000215:Acylation; D000388:Air; D002942:Circular Dichroism; D006801:Humans; D008051:Lipid Bilayers; D010743:Phospholipids / Q000737:chemistry; D011312:Pressure; D017433:Protein Structure, Secondary; D011510:Proteolipids / Q000737:chemistry* / Q000378:metabolism; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000378:metabolism; D011721:Pyrenes / Q000737:chemistry
D008051:Lipid Bilayers; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D011721:Pyrenes; C030984:pyrene