(515b) From Domain Size Distributions to Probing Lipid-Protein Interactions in Lung Surfactant Mixtures

The shape and size of a single domain in monolayers at coexistence has been shown to be a result of a balance of forces. Domain shape analysis of fluorescence images of a single or multi-component lipid monolayer can provide detailed information about the minimum energy radius, R0, the electric dipole density difference, m, and the line tension  between domains. Alterations in the domain size distribution of lipid monolayers in the presence of protein molecules may be used to analyze lipid-protein interactions in these systems. In this talk, we will present interactions between negatively charged lung surfactant monolayers and positively charged surfactant protein SP-B which together play an important role in the mechanism of breathing. By analyzing the domain size distribution we find that while the entropy of mixing plays a likely role in domain size distributions, addition of SP-B molecules reduces R0 as well as increases m. Our results therefore prove that SP-B alters the electrostatic interactions between domains by interacting with the negatively charged lipid monolayers.