Effect of hydrophobic surfactant proteins SP-B and SP-C on phospholipid monolayers. Protein structure studied using 2D IR and beta correlation analysis.
We have applied two-dimensional infrared (2D IR) and betanu correlation spectroscopy to in-situ IR spectroscopy of pulmonary surfactant proteins SP-B and SP-C in lipid-protein monolayers at the air-water interface. For both SP-B and SP-C, a statistical windowed autocorrelation method identified two separate surface pressure regions that contained maximum amide I intensity changes: 4-25 mN/m and 25-40 mN/m. For SP-C, 2D IR and betanu correlation analyses of these regions indicated that SP-C adopts a variety of secondary structure conformations, including alpha-helix, beta-sheet, and an intermolecular aggregation of extended beta-sheet structure. The main alpha-helix band split into two peaks at high surface pressures, indicative of two different helix conformations. At low surface pressures, all conformations of the SP-C molecule reacted identically to increasing surface pressure and reoriented in phase with each other. Above 25 mN/m, however, the increasing surface pressure selectively affected the coexisting protein conformations, leading to an independent reorientation of the protein conformations. The asynchronous 2D IR spectrum of SP-B showed the presence of two alpha-helix components, consistent with two separate populations of alpha-helix in SP-B-a hydrophobic fraction associated with the lipid chains and a hydrophilic fraction parallel to the membrane surface. The distribution of correlation intensity between the two alpha-helix cross peaks indicated that the more hydrophobic helix fraction predominates at low surface pressures whereas the more hydrophilic helix fraction predominates at high surface pressures. The different SP-B secondary structures reacted identically to increasing surface pressure, leading to a reorientation of all SP-B subunits in phase with one another.
D000388:Air; D000818:Animals; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D008055:Lipids / Q000737:chemistry; D015233:Models, Statistical; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry* / Q000378:metabolism*; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry* / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D017550:Spectroscopy, Fourier Transform Infrared; D013223:Statistics as Topic / Q000379:methods; D014867:Water
D008055:Lipids; D010715:Phosphatidylglycerols; D010743:Phospholipids; D037701:Pulmonary Surfactant-Associated Protein B; D037721:Pulmonary Surfactant-Associated Protein C; D014867:Water; C030345:1,2-dipalmitoylphosphatidylglycerol