This work reports the first x-ray scattering measurements to determine the effects of SP-B1-25, the N-terminus peptide of lung surfactant-specific protein SP-B, on the structure of palmitic acid (PA) monolayers. In-plane diffraction shows that the peptide fluidizes a portion of the monolayer but does not affect the packing of the residual ordered phase. This implies that the peptide resides in the disordered phase, and that the ordered phase is essentially pure lipid, in agreement with fluorescence microscopy studies. X-ray reflectivity shows that the peptide is oriented in the lipid monolayer at an angle of ∼56° relative to the interface normal, with one end protruding past the hydrophilic region into the fluid subphase and the other end embedded in the hydrophobic region of the monolayer. The quantitative insights afforded by this study lead to a better understanding of the lipid/protein interactions found in lung surfactant systems.
Bibliographical noteFunding Information:
We gratefully acknowledge beam time at HASYLAB at DESY, Hamburg, Germany, and funding by the programs DanSync (Denmark) and TMR of the European Community (contract ERBFMGECT950059). We thank Dr. Rita Hazal for a useful discussion and Dr. Mark Sherman of Beckman-The City of Hope Molecular Modeling Core Facility (Cancer Center Support grant P30 CA33572) for his assistance with the modeling of the SP-B 1–25 peptide at the palmitic acid monolayer. K.Y.C.L. is grateful for the support from the Camille and Henry Dreyfus New Faculty Award (NF-98–048), the March of Dimes Basil O’Connor Starter Scholar Research Award (5-FY98–0728), the American Lung Association (RG-085-N), and the David and Lucile Packard Foundation (99–1465). A.G. is supported by the Searle Scholars Program/the Chicago Community Trust (99-C-105). J.A.Z. and M.M.L. were supported by National Institutes of Health Grant HL51177. A.J.W. was supported by National Institutes of Health Grant HL55534. The Manuel Lujan Jr., Neutron Scattering Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences - Materials Science, under contract number W-7405-ENG-36 with the University of California. This work was also supported in part by the MRSEC Program of the National Science Foundation under Award Numbers DMR-9808595 (The University of Chicago) and DMR96–32716 (University of California, Santa Barbara).