Solubility versus Electrostatics: What Determines Lipid/Protein Interaction in Lung Surfactant

Mammalian lung surfactant is a complex lipid/protein mixture covering the alveolar interface and has the crucial function of reducing the surface tension at this boundary to minimal values. Surfactant protein SP-B plays an important role for this purpose and was the focus of many recent studies. However, the specificity of lipid/SP-B interactions is controversial. Since these investigations were accomplished at varying pH conditions (pH 5.5 and 7.0), we studied the specificity of these interactions in a dipalmitoylphosphatidylcholine (DPPC)/dipalmitoylphosphatidylglycerol (DPPG)/SP-B (4:1:0.2 mol %) model system at either pH. Mainly fluorescence microscopy and laterally resolved time-of-flight secondary ion mass spectrometry were used to reveal information about the phase behavior of the lipids and the molecular distribution of SP-B in the lipid mixture. DPPG forms separated condensed domains due to a strong hydrogen-bond network, from which the protein is mainly excluded. Considering the protein as an impurity of the lipid mixture leads to the principle of the zone melting process: an impurity is highly more soluble in a liquid phase than in a solid phase. The phase behavior effect of the lipids mainly outperforms the electrostatic interactions between DPPG and SP-B, leading to a more passively achieved colocalization of DPPC and SP-B

Walking the line: search behavior and foraging success in ant species

Finding food is one of the most important tasks an animal faces. Although the impact of behavior and morphology on individual foraging success is well characterized, an understanding of the extent of interspecific differences in these traits as well as their influence on resource competition is lacking. Temperate ant communities represent an ideal opportunity for examining how search behavior and morphology affect a species' ability to find food first because ant species demonstrate both a wide range of foraging patterns and intense interspecific competition for food resources. For 10 species across 2 communities, species-specific speed and turning rate were quantified by filming their foraging behavior in nature; we also measured the ratio of leg length to body length of their foragers. Food discovery ability was determined by observing which species found baits first when they were present in the immediate environment. Our results show that foraging patterns are species specific, suggesting that search behavior is an important component of niche separation in ant communities. We also suggest that ant species maximize discovery success at the community level using both behavioral and morphological mechanisms. Good discoverers moved in straighter lines, thereby possibly increasing their chances of finding food, and had longer legs relative to their body size, increasing their efficiency of movement. Copyright 2011, Oxford University Press.