LIPID AND PROTEIN EFFECTS ON MONOLAYER STABILITY

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A deficiency of surfactant at birth, often due to premature delivery, is responsible for neonatal respiratory distress syndrome (NRDS). Inactivation of lung surfactant, perhaps due to interactions with blood serum or proteins, is likely involved in the development of adult respiratory distress syndrome (ARDS). Alterations in the physical and/or chemical nature of lung surfactant often accompany damage from smoking and other diseases. The serious morbidity and mortality of these diseases necessitates that the role of surfactant in normal and diseased lungs be understood. We will examine three general hypotheses: (1) Specific interactions between SP-B and fatty acids common to lung surfactants result in more stable monolayers resistant to collapse. However, it is unclear whether the protein is present to retain the fatty acid in the monolayer, or vice versa. Similar interactions do not exist between unsaturated phosphatidylglycerols and SP-B, suggesting that the PG is "squeezed-out" on compression. (2) These specific protein-fatty acid interactions can be mimicked by simple polymer gegenions in solution or compromised by specific interactions with other charged proteins such as fibrinogen or albumin, or by lipids such as lysophosphatidylcholine which may result from disease-induced changes in the lung environment; and (3) A detailed structure-function relationship at the molecular level between the components of natural lung surfactants is necessary to begin a rational design of a purely synthetic lung surfactant to address these hypotheses, we will (1) determine the phase behavior of natural lung surfactant and its components using the Langmuir trough. In particular, we will attempt to understand the interactions of lung surfactant specific proteins with surfactant lipids that lead to enhanced collapse pressures and lower tensions; (2) construct a Brewster Angle Microscope capable of visualizing monolayer collapse at the air-water interface and on monolayers transferred to solid substances; (3) finish development of a polarized fluorescence microscope (PFM) to visualize phase separation in monolayers and localize fluorescent labelled SP-B proteins and peptides; (4) examine collapsed monolayers transferred to solid substrates with electron and atomic force microscopy. The monolayer work will be extended using a model system of collapse that is amenable to molecular resolution analysis via AFM of supported monolayers; (5) correlate our experimental work with theoretical models of the forces and interactions between model lipid and lipid-protein monolayers at the molecular level. This molecular level understanding is essential to designing new peptides to replace SP-B, which is currently the most costly and potentially hazardous component of replacement lung surfactants.