(502e) Effect of Hydrophobic Surfactant Proteins SP-B and SP-C On the Phase and Morphology of Protein Deficient Native Surfactant Films

We present alterations in the phase and morphology of a native replacement surfactant film induced either by the removal of the hydrophobic surfactant proteins from a commercially available replacement surfactant, Survanta, or by the systematic addition of bovine hydrophobic surfactant proteins SP-B and SP-C to the protein deficient Survanta lipid film. The surface tension lowering property of a native surfactant film is significantly compromised in the absence of the proteins, as is the ability of the film to undergo reversible collapse. A lack of proteins also causes the characteristic shoulder prevalent in most lung surfactant mixtures to disappear, illustrating the inability of the film to undergo reversible squeeze out by forming ?surface associated surfactant reservoirs?. Addition of SP-B causes an increase in the amount of material adsorbed from the sub-phase. Further it increases the monolayer stability and the compressibility modulus of film (i.e. decreases the compressibility of the film), thus helping the film achieve a high enough surface pressure during compression as well as quick re-absorption of material during expansion. On the other hand, SP-C plays a dominant role in the formation of bilayer patches containing unsaturated lipids. SP-C also changes the mechanisms of monolayer collapse, and the film collapses via the formation of reversible collapse cracks. However, it is only in the presence of both SP-B and SP-C that the monolayer films are able to perform all the biophysical functions necessary for the proper working of the lung surfactant. Our results explicate the role of the individual proteins in the lipid protein interactions associated with lung surfactant mixtures in a native system. Further, these observations provide conclusive evidence showing that both SP-B and SP-C are equally necessary for the long term survival of air-breathing mammals.