Hyperacidification of trans-Golgi network and endo/lysosomes in melanocytes by glucosylceramide-dependent V-ATPase activity.

Sphingolipids are considered to play a key role in protein sorting and membrane trafficking. In melanocytic cells, sorting of lysosomal and melanosomal proteins requires the sphingolipid glucosylceramide (GlcCer). This sorting information is located in the lumenal domain of melanosomal proteins.

Dynamic transbilayer lipid asymmetry.

Cells have thousands of different lipids. In the plasma membrane, and in membranes of the late secretory and endocytotic pathways, these lipids are not evenly distributed over the two leaflets of the lipid bilayer. The basis for this transmembrane lipid asymmetry lies in the fact that glycerolipids are primarily synthesized on the cytosolic and sphingolipids on the noncytosolic surface of cellular membranes, that cholesterol has a higher affinity for sphingolipids than for glycerolipids.

Homo-FRET imaging as a tool to quantify protein and lipid clustering.

Homo-FRET, Förster resonance energy transfer between identical fluorophores, can be conveniently measured by observing its effect on the fluorescence anisotropy. This review aims to summarize the possibilities of fluorescence anisotropy imaging techniques to investigate clustering of identical proteins and lipids. Homo-FRET imaging has the ability to determine distances between fluorophores.

Cholesterol, the central lipid of mammalian cells.

Despite its importance for mammalian cell biology and human health, there are many basic aspects of cholesterol homeostasis that are not well understood. Even for the well-characterized delivery of cholesterol to cells via lipoproteins, a novel regulatory mechanism has been discovered recently, involving a serum protein called PCSK9, which profoundly affects lipoproteins and their receptors. Cells can export cholesterol by processes that require the activity of ABC transporters, but the molecular mechanisms for cholesterol transport remain unclear.

Membranes in motion.

The Keystone Symposium on the Molecular Basis for Biological Membrane Organization and Dynamics held in January this year offered new insights into the molecular machines at work in cells. Topics included the machinery responsible for the dynamic shape of organelles, the budding and fusion of vesicular carriers, and the intricate sorting systems that ensure the correct delivery of cellular components.

Sphingolipid topology and the dynamic organization and function of membrane proteins.

When acquiring internal membranes and vesicular transport, eukaryotic cells started to synthesize sphingolipids and sterols. The physical differences between these and the glycerophospholipids must have enabled the cells to segregate lipids in the membrane plane. Localizing this event to the Golgi then allowed them to create membranes of different lipid composition, notably a thin, flexible ER membrane, consisting of glycerolipids, and a sturdy plasma membrane containing at least 50% sphingolipids and sterols.

Synaptobrevin, sphingolipids, and secretion: lube 'n' go at the synapse.

For neurotransmitter release to occur, proteins and lipids have to work together. The classical view of this process is that a variety of proteins work hard to force the unwilling, fusion-aversive lipids into merging. In this issue of Neuron, a study by Darios et al.

Protein-lipid interactions: paparazzi hunting for snap-shots.

Photoactivatable groups meeting the criterion of minimal perturbance allow the investigation of interactions in biological samples. Here, we review the application of photoactivatable groups in lipids enabling the study of protein-lipid interactions in (biological) membranes. The chemistry of various photoactivatable groups is summarized and the specificity of the interactions detected is discussed.

Update of the LIPID MAPS comprehensive classification system for lipids.

In 2005, the International Lipid Classification and Nomenclature Committee under the sponsorship of the LIPID MAPS Consortium developed and established a "Comprehensive Classification System for Lipids" based on well-defined chemical and biochemical principles and using an ontology that is extensible, flexible, and scalable. This classification system, which is compatible with contemporary databasing and informatics needs, has now been accepted internationally and widely adopted. In response to considerable attention and requests from lipid researchers from around the globe and in a variety of fields, the comprehensive classification system has undergone significant revisions over the last few years to more fully represent lipid structures from a wider variety of sources and to provide additional levels of detail as necessary.

Sphingolipid management by an orchestra of lipid transfer proteins.

The various membranes in eukaryotic cells have unique lipid compositions. Despite important discoveries in lipid research over recent decades, the basic principles by which cells define their membrane compositions are essentially unknown. Cells must sense the concentration of each lipid, integrate such signals and regulate the activity of their metabolic enzymes and transport routes to dynamically meet their needs in terms of membrane composition.

Glycolipid-dependent sorting of melanosomal from lysosomal membrane proteins by lumenal determinants.

Melanosomes are lysosome-related organelles that coexist with lysosomes in mammalian pigment cells. Melanosomal and lysosomal membrane proteins share similar sorting signals in their cytoplasmic tail, raising the question how they are segregated. We show that in control melanocytes, the melanosomal enzymes tyrosinase-related protein 1 (Tyrp1) and tyrosinase follow an intracellular Golgi to melanosome pathway, whereas in the absence of glycosphingolipids, they are observed to pass over the cell surface.

Membrane lipids: where they are and how they behave.

Throughout the biological world, a 30 A hydrophobic film typically delimits the environments that serve as the margin between life and death for individual cells. Biochemical and biophysical findings have provided a detailed model of the composition and structure of membranes, which includes levels of dynamic organization both across the lipid bilayer (lipid asymmetry) and in the lateral dimension (lipid domains) of membranes. How do cells apply anabolic and catabolic enzymes, translocases and transporters, plus the intrinsic physical phase behaviour of lipids and their interactions with membrane proteins, to create the unique compositions and multiple functionalities of their individual membranes?

The way we view cellular (glyco)sphingolipids.

Mammalian cells synthesize ceramide in the endoplasmic reticulum (ER) and convert this to sphingomyelin and complex glycosphingolipids on the inner, non-cytosolic surface of Golgi cisternae. From there, these lipids travel towards the outer, non-cytosolic surface of the plasma membrane and all membranes of the endocytic system, where they are eventually degraded. At the basis of the selective, anterograde traffic out of the Golgi lies the propensity of the sphingolipids to self-aggregate with cholesterol into microdomains termed 'lipid rafts'.

The European lipidomics initiative: enabling technologies.

Lipidomics is a new term to describe a scientific field that is a lot broader than lipidology, the science of lipids. Besides lipidology, lipidomics covers the lipid-metabolizing enzymes and lipid transporters, their genes and regulation; the quantitative determination of lipids in space and time, and the study of lipid function. Because lipidomics is concerned with all lipids and their enzymes and genes, it faces the formidable challenge to develop enabling technologies to comprehensively measure the expression, location, and regulation of lipids, enzymes, and genes in time, including high-throughput applications.

Pre- and post-Golgi translocation of glucosylceramide in glycosphingolipid synthesis.

Glycosphingolipids are controlled by the spatial organization of their metabolism and by transport specificity. Using immunoelectron microscopy, we localize to the Golgi stack the glycosyltransferases that produce glucosylceramide (GlcCer), lactosylceramide (LacCer), and GM3. GlcCer is synthesized on the cytosolic side and must translocate across to the Golgi lumen for LacCer synthesis.

Analysis of detergent-resistant membranes associated with apical and basolateral GPI-anchored proteins in polarized epithelial cells.

Detergent-resistant membranes (DRMs) represent specialized membrane domains resistant to detergent extraction, which may serve to segregate proteins in a specific environment in order to improve their function. Segregation of glycosylphosphatidylinositol-anchored proteins (GPI-APs) in DRMs has been shown to be involved in their sorting to the apical membrane in polarized epithelial cells. Nonetheless, we have shown that both apical and basolateral GPI-APs associate with DRMs.

Gangliosides play an important role in the organization of CD82-enriched microdomains.

Four-transmembrane-domain proteins of the tetraspanin superfamily are the organizers of specific microdomains at the membrane [TERMs (tetraspanin-enriched microdomains)] that incorporate various transmembrane receptors and modulate their activities. The structural aspects of the organization of TERM are poorly understood. In the present study, we investigated the role of gangliosides in the assembly and stability of TERM.

ABC lipid transporters: extruders, flippases, or flopless activators?

Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracellular aqueous milieu. Because the desorption from the membrane costs more energy than provided by two ATPs, the transporter probably only translocates the lipid to a partially hydrophilic site on its extracellular face. From this high-energy site, the lipid may efficiently move to the acceptor, which ideally is bound to the transporter, or, in the absence of an acceptor, fall back into the membrane.

Cellular lipidomics.

The cellular lipidome comprises over 1000 different lipids. Most lipids look similar having a polar head and hydrophobic tails. Still, cells recognize lipids with exquisite specificity.

Membrane curvature sorts lipids. Stabilized lipid rafts in membrane transport.

Stabilized lipid rafts in membrane transport