Effect of hydrophobic surfactant proteins SP-B and SP-C on phospholipid monolayers. Protein structure studied using 2D IR and βv correlation analysis

Academic Article

Abstract

  • We have applied two-dimensional infrared (2D IR) and βv 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 βv correlation analyses of these regions indicated that SP-C adopts a variety of secondary structure conformations, including α-helix, β-sheet, and an intermolecular aggregation of extended β-sheet structure. The main α-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 α-helix components, consistent with two separate populations of α-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 α-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.
  • Authors

    Published In

    Digital Object Identifier (doi)

    Author List

  • Shanmukh S; Howell P; Baatz JE; Dluhy RA
  • Start Page

  • 2126
  • End Page

  • 2141
  • Volume

  • 83
  • Issue

  • 4