Solubility of hydrophobic surfactant proteins in organic solvent/water mixtures. Structural studies on SP-B and SP-C in aqueous organic solvents and lipids.
The solubility of hydrophobic pulmonary surfactant proteins in different organic solvents and organic solvent/water combinations has been analyzed. Three organic solvents have been selected: methanol (MetOH), acetonitrile (ACN) and trifluoroethanol (TFE). Porcine SP-B showed very similar calculated secondary structure when dissolved in methanol, 60% ACN or 70% TFE and reconstituted in lysophosphatidylcholine (LPC) micelles or dipalmitoylphosphatidylcholine (DPPC) vesicles, as deduced from circular dichroism studies. SP-B was calculated to possess around 45% of alpha-helix in all these systems. The fluorescence emission spectrum of SP-B has been also characterized in aqueous solvents and lipids. It always showed a splitting of the tryptophan contribution into two components with different emission maxima. SP-C had a very different structure in 80% ACN or 70% TFE. While alpha-helix was the main secondary structure of SP-C in ACN/water mixtures--around 50%--, it had almost exclusively beta-structure when dissolved in 70% TFE. The CD spectrum of SP-C in TFE showed dependence on the protein concentration, suggesting that protein-protein interactions could be important in this beta-conformation. SP-C reconstituted in LPC micelles or DPPC vesicles had a CD spectrum qualitatively similar to that one in aqueous ACN, with a dominant alpha-helical structure. The alpha-helical content of SP-C in micelles of LPC and vesicles of DPPC, 60 and 70%, respectively, was calculated to be higher than the alpha-helical content of the protein dissolved in any aqueous organic solvent.
Pérez-Gil
J
J
Dept Bioquímica y Biología Molecular I, Fac. Ciencias Químicas, Universidad Complutense de Madrid, Spain.
Cruz
A
A
Casals
C
C
D015060:1,2-Dipalmitoylphosphatidylcholine; D000097:Acetonitriles; D000595:Amino Acid Sequence; D000818:Animals; D000432:Methanol; D008823:Micelles; D008969:Molecular Sequence Data; D011510:Proteolipids / Q000737:chemistry* / Q000302:isolation & purification; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000302:isolation & purification; D012995:Solubility; D012997:Solvents; D013552:Swine; D014270:Trifluoroethanol; D014867:Water
D000097:Acetonitriles; D008823:Micelles; D011510:Proteolipids; D011663:Pulmonary Surfactants; D012997:Solvents; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D014270:Trifluoroethanol; D000432:Methanol; C032159:acetonitrile