A dansylated form of porcine surfactant-associated protein C (Dns-SP-C), bearing a single dansyl group at its N-terminal end, has been used to characterize the lipid–protein and protein–protein interactions of SP-C reconstituted in phospholipid bilayers, using fluorescence spectroscopy. The fluorescence emission spectrum of Dns-SP-C in phospholipid bilayers is similar to the spectrum of dansyl-phosphatidylethanolamine, and indicates that the N-terminal end of the protein is located at the surface of the membranes and is exposed to the aqueous environment. In membranes containing phosphatidylglycerol (PG), the fluorescence of Dns-SP-C shows a 3-fold increase with respect to the fluorescence of phosphatidylcholine (PC), suggesting that electrostatic lipid–protein interactions induce important effects on the structure and disposition of the N-terminal segment of the protein in these membranes. This effect saturates above 20% PG molar content in the bilayers. The parameters for the interaction of Dns-SP-C with PC or PG have been estimated from the changes induced in the fluorescence emission spectrum of the protein. The protein had similar Kd values for its interaction with the different phospholipids tested, of the order of a few micromolar. Cooling of Dns-SP-C-containing dipalmitoyl PC bilayers to temperatures below the phase transition of the phospholipid produced a progressive blue-shift of the fluorescence emission of the protein. This effect is interpreted as a consequence of the transfer of the N-terminal segment of the protein into less polar environments that originate during protein lateral segregation. This suggests that conformation and interactions of the N-terminal segment of SP-C could be important in regulating the lateral distribution of the protein in surfactant bilayers and monolayers. Potential SP-B–SP-C interactions have been explored by analysing fluorescence resonance energy transfer (RET) from the single tryptophan in porcine SP-B to dansyl in Dns-SP-C. RET has been detected in samples where native SP-B and Dns-SP-C were concurrently reconstituted in PC or PG bilayers. However, the analysis of the dependence of RET on the protein density excluded specific SP-B–Dns-SP-C associations.
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November 2001
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Research Article|
October 25 2001
Superficial disposition of the N-terminal region of the surfactant protein SP-C and the absence of specific SP-B–SP-C interactions in phospholipid bilayers
Inés PLASENCIA;
Inés PLASENCIA
Departamento de Bioquímica, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
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Antonio CRUZ;
Antonio CRUZ
Departamento de Bioquímica, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
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Cristina CASALS;
Cristina CASALS
Departamento de Bioquímica, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
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Jesús PÉREZ-GIL
Jesús PÉREZ-GIL
1
Departamento de Bioquímica, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
1To whom correspondence should be addressed (e-mail perejil@solea.quim.ucm.es).
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Publisher: Portland Press Ltd
Received:
March 12 2001
Revision Received:
July 02 2001
Accepted:
August 28 2001
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2001
2001
Biochem J (2001) 359 (3): 651–659.
Article history
Received:
March 12 2001
Revision Received:
July 02 2001
Accepted:
August 28 2001
Citation
Inés PLASENCIA, Antonio CRUZ, Cristina CASALS, Jesús PÉREZ-GIL; Superficial disposition of the N-terminal region of the surfactant protein SP-C and the absence of specific SP-B–SP-C interactions in phospholipid bilayers. Biochem J 1 November 2001; 359 (3): 651–659. doi: https://doi.org/10.1042/bj3590651
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