Solubility versus electrostatics: what determines lipid/protein interaction in lung surfactant.
Mammalian lung surfactant is a complex lipid/protein mixture covering the alveolar interface and has the crucial function of reducing the surface tension at this boundary to minimal values. Surfactant protein SP-B plays an important role for this purpose and was the focus of many recent studies. However, the specificity of lipid/SP-B interactions is controversial. Since these investigations were accomplished at varying pH conditions (pH 5.5 and 7.0), we studied the specificity of these interactions in a dipalmitoylphosphatidylcholine (DPPC)/dipalmitoylphosphatidylglycerol (DPPG)/SP-B (4:1:0.2 mol %) model system at either pH. Mainly fluorescence microscopy and laterally resolved time-of-flight secondary ion mass spectrometry were used to reveal information about the phase behavior of the lipids and the molecular distribution of SP-B in the lipid mixture. DPPG forms separated condensed domains due to a strong hydrogen-bond network, from which the protein is mainly excluded. Considering the protein as an impurity of the lipid mixture leads to the principle of the zone melting process: an impurity is highly more soluble in a liquid phase than in a solid phase. The phase behavior effect of the lipids mainly outperforms the electrostatic interactions between DPPG and SP-B, leading to a more passively achieved colocalization of DPPC and SP-B.
Seifert
M
M
Institute of Biochemistry and Tascon GmbH, 48149 Münster, Germany.
Breitenstein
D
D
Klenz
U
U
Meyer
M C
MC
Galla
H-J
HJ
D000731:Androstanes / Q000737:chemistry*; D005453:Fluorescence; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D018625:Microscopy, Atomic Force; D044367:Phase Transition; D010715:Phosphatidylglycerols / Q000737:chemistry*; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry*; D012995:Solubility; D055672:Static Electricity; D013500:Surface Tension
C415601:3-oxo-androstan-17-yl-(2'',2'',6'',6''-tetramethyl-N-oxyl)piperidyl butan-1',4'-dioate; D000731:Androstanes; D010715:Phosphatidylglycerols; D037701:Pulmonary Surfactant-Associated Protein B; D011663:Pulmonary Surfactants; C030345:1,2-dipalmitoylphosphatidylglycerol