Dept. of Chemistry
Oregon Graduate Institute of Science & Technology
Molecular recognition of chemistry at organized interfaces often leads to interfacial self-assembly. Because many have evolved natural functions for membrane recognition, proteins are logical components to probe both interfacial reactivity and the self-organization of large molecules. In this study, phospholipase A[subscript 2] (PLA[subscript 2]) and lung surfactant have been investigated with physical methods to determine the influence of interfacial properties on protein self-assembly and membrane organization. Biomembrane models at the air-water interface were used to alter the interfacial chemistry responsible for organization. Protein-membrane interactions were analyzed using monolayer film balance techniques and fluorescence microscopy at the air-water interface. Results show that macromolecules such as biopolymers will form large two-dimensional aggregates under conditions which favor specific protein binding and assembly. PLA[subscript 2] was observed to form large two-dimensional domains during phospholipid hydrolysis. PLA[subscript 2]-catalyzed phospholipid hydrolysis produces lyso-lipid and free fatty acid reaction products. PLA[subscript 2] self-assembly in model lipid monolayer systems results from interfacial fatty acid reaction product lateral phase separation. PLA[subscript 2] self-assembly occurred only under conditions where fatty acid phase separation was observed: the presence of Ca[superscript 2+] and alkaline pH. PLA[subscript 2] self-assembly was mimicked using a water-soluble cationic dye as a protein analog. Results from mimicry studies indicate that, in addition to phase-separated fatty acids, chiral lipids also play an important role in determining self-assembled protein structural morphology. Lung surfactant monolayers comprising mixed lipids and peptides were also investigated to determine structure-function relationships between lipids and membrane-resident, hydrophobic surfactant protein. Lung surfactant extract and purified subfraction monolayers were prepared to determine the effects of individual surfactant components on interfacial lung surfactant structure. Lung surfactant monolayer microstructure is sensitive to the presence of proteins and cholesterol-based lipids. These results suggest that protein and cholesterol-based lipid contents in lung surfactant affect the lateral organization of the major lipid components in lung surfactant, 1,2-dipalmitoylphosphatidylcholine and 1-palmitoyl,2-myristoylphosphatidylcholine.
Maloney, Kevin Maurice, "Protein interactions with model phospholipid monolayers at the air-liquid interface" (1995). Scholar Archive. 168.