Several methods of measuring the line tension between phase-separated liquid-ordered–liquid -disordered domains in phospholipid–cholesterol systems have been proposed. These experimental techniques are typically internally self-consistent, but the measured line tension values vary widely among these techniques. To date, no measurement of line tension has utilized multiple experimental techniques to look at the same monolayer system. Here we compare two nonperturbative methods, Fourier analysis of boundary fluctuations (BA) and one proposed by Israelachvili involving the analysis of domain size distributions (SD), to extract the line tension in a 70 mol % DMPC/30 mol % dihydrocholesterol (DChol) mixture as a function of surface pressure. We show that BA predicts the expected variation in line tension measurements consistent with the theoretical critical exponent whereas SD does not. From this comparison, we conclude that the size distribution of monolayer domains is metastable and primarily determined by the kinetics of domain nucleation and subsequent aging.

The binding of lectins to glycan receptors on the host cell surface is a key step contributing to the virulence and species specificity of most viruses. This is exemplified by the viral protein hemagglutinin (HA) of the influenza A virus, whose binding specificity is modulated by the linkage pattern of terminal sialic acids on glycan receptors of host epithelial cells. Such specificity dictates whether transmission is confined to a particular animal species or jumps between species. Here we show, using H5N1 avian influenza as a model, that the specific binding of recombinant HA to a2-3 linked sialic acids can be enhanced dramatically by interaction with the surface of the lipid membrane. This effect can be quantitatively accounted for by a two-stage process in which weak association of HA with the membrane surface precedes more specific and tighter binding to the glycan receptor. The weak protein-membrane interaction discovered here in the model system may play an important secondary role in the infection and pathogenesis of the influenza A virus.