Resolution of inflammation is essential for tissue homeostasis and a promising approach to inflammatory disorders. Here we found that DEL-1, a secreted protein inhibiting leukocyte-endothelial adhesion and inflammation initiation, also functions as a non-redundant downstream effector in inflammation clearance. In human and murine periodontitis, waning of inflammation correlated with DEL-1 upregulation, whereas resolution of experimental periodontitis failed in DEL-1 deficiency. This concept was mechanistically substantiated in acute monosodium urate crystal-induced inflammation, where the pro-resolution function of DEL-1 was attributed to effective apoptotic neutrophil clearance (efferocytosis). DEL-1-mediated efferocytosis induced liver-X-receptor-dependent macrophage reprogramming to pro-resolving phenotype and was required for optimal production of at least certain specific pro-resolving mediators. Experiments in transgenic mice with cell-specific overexpression of DEL-1 linked its anti-leukocyte recruitment action to endothelial-derived DEL-1 and its efferocytic/pro-resolving action to macrophage-derived DEL-1. Thus, the compartmentalized expression of DEL-1 facilitates distinct homeostatic functions in an appropriate context that can be harnessed therapeutically.

This review focuses on structure and functions of spectrin as a major component of the membrane skeleton. Recent advances on spectrin function as an interface for signal transduction mediation and a number of data concerning interaction of spectrin with membrane channels, adhesion molecules, receptors and transporters draw a picture of multifaceted protein. Here, we attempted to show the current depiction of multitask role of spectrin in cell physiology. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.

It is well documented that activation of calpain, a calcium-sensitive cysteine protease, marks the pathology of naturally and experimentally occurring neurodegenerative conditions. Calpain-mediated proteolysis of major membrane-skeletal protein, alphaII-spectrin, results in the appearance of two unique and highly stable breakdown products, which is an early event in neural cell pathology. This review focuses on spectrin degradation by calpain within neurons induced by diverse conditions, emphasizing a current picture of multi-pattern neuronal death and a recent success in the development of spectrin-based biomarkers. The issue is presented in the context of the major structural and functional properties of the two proteins.

We report a synthetic biology-inspired approach for the engineering of amphipathic DNA origami structures as membrane-scaffolding tools. The structures have a flat membrane-binding interface decorated with cholesterol-derived anchors. Sticky oligonucleotide overhangs on their side facets enable lateral interactions leading to the formation of ordered arrays on the membrane. Such a tight and regular arrangement makes our DNA origami capable of deforming free-standing lipid membranes, mimicking the biological activity of coat-forming proteins, for example, from the I-/F-BAR family.

Recently, DNA origami became a powerful tool for custom-shaped functional biomolecules. In this paper, we present the first approach towards assembling amphipathic three-dimensional DNA origami nanostructures and assessing their dynamics on the surface of freestanding phospholipid membranes. Our nanostructures were stiff DNA origami rods comprising six DNA helices. They were functionalized with hydrophobic cholesteryl-ethylene glycol anchors and fluorescently labeled at defined positions. Having these tools in hand, we could demonstrate not only the capability of the amphipathic nanorods to coat membranes of various phospholipid compositions, but also their switchable liquid-ordered/liquid-disordered partitioning on phase separated membranes. The observed translocation of our nanostructures between different domains was controlled by divalent ions. Moreover, selective fluorescent labeling enabled us to distinguish between the translational and rotational diffusion of our six helix bundles on the membranes by fluorescence correlation spectroscopy. The obtained data reveal how DNA origami can be employed as a valuable tool in membrane biophysics.

The orchestrated recognition of phosphoinositides and concomitant intracellular release of Ca2+ is pivotal to almost every aspect of cellular processes, including membrane homeostasis, cell division and growth, vesicle trafficking, as well as secretion. Although Ca2+ is known to directly impact phosphoinositide clustering, little is known about the molecular basis for this or its significance in cellular signaling. Here, we study the direct interaction of Ca2+ with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), the main lipid marker of the plasma membrane. Electrokinetic potential measurements of PI(4,5)P2 containing liposomes reveal that Ca2+ as well as Mg2+ reduce the zeta potential of liposomes to nearly background levels of pure phosphatidylcholine membranes. Strikingly, lipid recognition by the default PI(4,5)P2 lipid sensor, phospholipase C delta 1 pleckstrin homology domain (PLC δ1-PH), is completely inhibited in the presence of Ca2+, while Mg2+ has no effect with 100 nm liposomes and modest effect with giant unilamellar vesicles. Consistent with biochemical data, vibrational sum frequency spectroscopy and atomistic molecular dynamics simulations reveal how Ca2+ binding to the PI(4,5)P2 headgroup and carbonyl regions leads to confined lipid headgroup tilting and conformational rearrangements. We rationalize these findings by the ability of calcium to block a highly specific interaction between PLC δ1-PH and PI(4,5)P2, encoded within the conformational properties of the lipid itself. Our studies demonstrate the possibility that switchable phosphoinositide conformational states can serve as lipid recognition and controlled cell signaling mechanisms.

Over the last decade, functionally designed DNA nanostructures applied to lipid membranes prompted important achievements in the fields of biophysics and synthetic biology. Taking advantage of the universal rules for self-assembly of complementary oligonucleotides, DNA has proven to be an extremely versatile biocompatible building material on the nanoscale. The possibility to chemically integrate functional groups into oligonucleotides, most notably with lipophilic anchors, enabled a widespread usage of DNA as a viable alternative to proteins with respect to functional activity on membranes. As described throughout this review, hybrid DNA-lipid nanostructures can mediate events such as vesicle docking and fusion, or selective partitioning of molecules into phase-separated membranes. Moreover, the major benefit of DNA structural constructs, such as DNA tiles and DNA origami, is the reproducibility and simplicity of their design. DNA nanotechnology can produce functional structures with subnanometer precision and allow for a tight control over their biochemical functionality, e.g., interaction partners. DNA-based membrane nanopores and origami structures able to assemble into two-dimensional networks on top of lipid bilayers are recent examples of the manifold of complex devices that can be achieved. In this review, we will shortly present some of the potentially most relevant avenues and accomplishments of membrane-anchored DNA nanostructures for investigating, engineering, and mimicking lipid membrane-related biophysical processes.

Phosphatidic acid (PA) is the simplest glycerophospholipid naturally occurring in living organisms, and even though its content among other cellular lipids is minor, it is drawing more and more attention due to its multiple biological functions. PA is a precursor for other phospholipids, acts as a lipid second messenger and, due to its structural properties, is also a modulator of membrane shape. Although much is known about interaction of PA with its effectors, the molecular mechanisms remain unresolved to a large degree. Throughout many of the well-characterized PA cellular sensors, no conserved binding domain can be recognized. Moreover, not much is known about the cellular dynamics of PA and how it is distributed among subcellular compartments. Remarkably, PA can play distinct roles within each of these compartments. For example, in the nucleus it behaves as a mitogen, influencing gene expression regulation, and in the Golgi membrane it plays a role in membrane trafficking. Here, we discuss how a biophysical experimental approach enabled PA behavior to be described in the context of a lipid bilayer and to what extent various physicochemical conditions may modulate the functional properties of this lipid. Understanding these aspects would help to unravel specific mechanisms of PA-driven membrane transformations and protein recruitment and thus would lead to a clearer picture of the biological role of PA.