Effect of pulmonary surfactant protein XXXX on the micro- and nanostructure of phospholipid films.

@entity4748 @entity397 @entity25097 @entity40680 @entity4747
Monolayers of @entity4747 ( @entity4748 ) and @entity4748 / @entity40680 ( @entity40680 ) (7:3, w/w) in the absence or in the presence of 2, 5, 10, or 20 weight percent of porcine surfactant protein @entity25097 were spread at the air-liquid interface of a surface balance, compressed up to surface pressures in the liquid-expanded/liquid-condensed (LE-LC) plateau of the isotherm, transferred onto mica supports, and analyzed by scanning force microscopy. In the absence of protein, the films showed micrometer-sized condensed domains with morphology and size that were analogous to those observed in situ at the air-liquid interface by epifluorescence microscopy. Scanning force microscopy permits examination of the coexisting phases at a higher resolution than previously achieved with fluorescent microscopy. Both LE and LC regions of @entity4748 films were heterogeneous in nature. LC microdomains contained numerous expanded-like islands whereas regions apparently liquid-expanded were covered by a condensed-like framework of interconnected nanodomains. Presence of increasing amounts of pulmonary surfactant protein @entity25097 affected the distribution of the LE and LC regions of @entity4748 and @entity4748 / @entity40680 films both at the microscopic and the nanoscopic level. The condensed microdomains became more numerous but their size decreased, resulting in an overall reduction of the amount of total LC phase in both @entity4748 and @entity4748 / @entity40680 films. At the nanoscopic level, @entity25097 also caused a marked reduction of the size of the condensed-like nanodomains in the LE phase and an increase in the length of the LE/LC interface. @entity25097 promotes a fine nanoscopic framework of lipid and lipid-protein nanodomains that is associated with a substantial mechanical resistance to film deformation and @entity397 as observed during film transference and manipulation. The effect of @entity25097 on the nanoscopic structure of the lipid films was greater in @entity4748 / @entity40680 than in pure @entity4748 films, indicating additional contributions of electrostatic lipid-protein interactions. The alterations of the nanoscopic structures of phospholipid films by @entity25097 provide the structural framework for the protein simultaneously sustaining structural stability as well as dynamical flexibility in surfactant films at the extreme conditions imposed by the respiratory mechanics. @entity25097 also formed segregated two-dimensional clusters that were associated with the boundaries between LC microdomains and the LE regions of @entity4748 and @entity4748 / @entity40680 films. The presence of these clusters at protein-to-lipid proportions above 2% by weight suggests that the concentration of @entity25097 in the surfactant lipid-protein complexes may be close to the solubility limit of the protein in the lipid films.
