Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors.

The Nem1–Spo7 complex in the yeast Saccharomyces cerevisiae is a protein phosphatase that catalyzes the dephosphorylation of Pah1 phosphatidate phosphatase required for its translocation to the nuclear/endoplasmic reticulum membrane. The Nem1–Spo7/Pah1 phosphatase cascade plays a major role in triacylglycerol synthesis and in the regulation of phospholipid synthesis. In this work, we examined Spo7, a regulatory subunit required for Nem1 catalytic function, to identify residues that govern formation of the Nem1–Spo7 complex.  By deletion analysis of Spo7, we identified a hydrophobic Leu–Leu-Ile (LLI) sequence comprising residues 54–56 as being required for the protein to complement the temperature-sensitive phenotype of a spo7Δ mutant strain. Mutational analysis of the LLI sequence with alanine and arginine substitutions showed that its overall hydrophobicity is crucial for the formation of the Nem1–Spo7 complex as well as for the Nem1 catalytic function on its substrate Pah1 in vivo.  Consistent with the role of the Nem1–Spo7 complex in activating the function of Pah1, we found that the mutational effects of the Spo7 LLI sequence were on the Nem1–Spo7/Pah1 axis that controls lipid synthesis and related cellular processes (e.g. triacylglycerol/phospholipid synthesis, lipid droplet formation, nuclear/endoplasmic reticulum membrane morphology, vacuole fusion, and growth on glycerol medium). These findings advance the understanding of the Nem1–Spo7 complex formation and its role in the phosphatase cascade that regulates the function of Pah1 phosphatidate phosphatase.

function of LDs. While much work has focused on peripheral and integral membrane proteins, the mechanism by which LD binding proteins recognize and target to LDs is still poorly understood (1). This is especially true for dedicated LD binding proteins of the perilipin family, i.e., perilipin 1 through 5, that function in the biogenesis and metabolism (lipolysis) of LDs. No work has directly investigated the interaction of a perilipin family member with a phospholipid monolayer interface. In order to address how this family of proteins interacts with lipid interfaces, we investigated the interaction of perilipin 3 with phospholipid monolayers at the air-buffer interface. We chose perilipin 3 because it is found in the cytosol as well as on the LD surface, and because previous work has characterized the structure and LD association of the protein (1-3).In addition to providing cellular energy, LDs take part in many other cellular functions, including signal transduction, formation of new cellular membranes, hormone synthesis, and lipid trafficking (4-8). Under certain physiological conditions, LDs have been found to act as storehouses for several different types of enzymes and proteins, including histones (9, 10), and they also facilitate virus replication (11-13). An understanding of how proteins Lipid droplets (LDs) are dynamic cell organelles that carry out a multitude of cellular functions vital for life, and protein-lipid interactions are crucial to the structure and

Lipid droplets are "small" organelles that play an important role in de novo synthesis of new membrane, and steroid hormones, as well as in energy storage. The way proteins interact specifically with the oil-(phospho-)lipid monolayer interface of lipid droplets is a relatively unexplored but crucial question. Here, we use our home built liquid droplet tensiometer to mimic intracellular lipid droplets and study protein-lipid interactions at this interface. As model neutral lipid binding protein, we use apoLp-III, an amphipathic α-helix bundle protein. This domain is also found in proteins from the perilipin family and in apoE. Protein binding to the monolayer is studied by the decrease in the oil/water surface tension. Previous work used POPC (one of the major lipids found on lipid droplets) to form the phospholipid monolayer on the triolein surface. Here we expand this work by incorporating other lipids with different physico-chemical properties to study the effect of charge and lipid head-group size. This study sheds light on the affinity of this important protein domain to interact with lipids.

Neutral lipid transport in mammals is complicated involving many types of apolipoprotein. The exchangeable apolipoproteins mediate the transfer of hydrophobic lipids between tissues and particles, and bind to cell surface receptors. Amphipathic α-helices form a common structural motif that facilitates their lipid binding and exchangeability. ApoLp-III, the only exchangeable apolipoprotein found in insects, is a model amphipathic α-helix bundle protein and its three dimensional structure and function mimics that of the mammalian proteins apoE and apoAI. Even the intracellular exchangeable lipid droplet protein TIP47/perilipin 3 contains an α-helix bundle domain with high structural similarity to that of apoE and apoLp-III. Here, we investigated the interaction of apoLp-III from Locusta migratoria with lipid monolayers. Consistent with earlier work we find that insertion of apoLp-III into fluid lipid monolayers is highest for diacylglycerol. We observe a preference for saturated and more highly ordered lipids, suggesting a new mode of interaction for amphipathic α-helix bundles. X-ray reflectivity shows that apoLp-III unfolds at a hydrophobic interface and flexible loops connecting the amphipathic α-helices stay in solution. X-ray diffraction indicates that apoLp-III insertion into diacylglycerol monolayers induces additional ordering of saturated acyl-chains. These results thus shed important new insight into the protein-lipid interactions of a model exchangeable apolipoprotein with significant implications for its mammalian counterparts.