title: Conformational changes in SP-B as a function of surface pressure.
abstract: X-ray reflectivity of bovine and sheep surfactant-associated protein B (SP-B) monolayers is used in conjunction with pressure-area isotherms and protein models to suggest that the protein undergoes changes in its tertiary structure at the air/water interface under the influence of surface pressure, indicating the likely importance of such changes to the phenomena of protein squeeze out as well as lipid exchange between the air-water interface and subphase structures. We describe an algorithm based on the well-established box- or layer-models that greatly assists the fitting of such unknown scattering-length density profiles, and which takes the available instrumental resolution into account. Scattering-length density profiles from neutron reflectivity of bovine SP-B monolayers on aqueous subphases are shown to be consistent with the exchange of a large number of labile protons as well as the inclusion of a significant amount of water, which is partly squeezed out of the protein monolayer at elevated surface pressures.
mesh_terms: D000818:Animals; D002417:Cattle; D003198:Computer Simulation; D008958:Models, Molecular; D033363:Neutron Diffraction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry* / Q000145:classification; D012756:Sheep; D012996:Solutions; D013045:Species Specificity; D013500:Surface Tension; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D037701:Pulmonary Surfactant-Associated Protein B; D012996:Solutions; D014867:Water