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Cholesterol regulation of ion channels and receptors
Examines new research on the role of cholesterol in regulating ion channels and receptors and its effect on health
Drawing together and analyzing all the latest research findings, this book explores the role of cholesterol in the regulation of ion channels and receptors, including its pathological effects. It is the first book to comprehensively describe the complex mechanisms by which cholesterol regulates two major classes of membrane proteins. Moreover, it sheds new light on how cholesterol affects essential cellular functions such as the contraction of the heart, propagation of nerve impulses, and regulation of blood pressure and kidney function.
Written and edited by leading pioneers in the field, Cholesterol Regulation of Ion Channels and Receptors is divided into three parts:
* Part I, Cholesterol Regulation of Membrane Properties, introduces the heterogeneity of cholesterol distribution in biological membranes and the physical and biological implications of the formation of cholesterol-rich membrane domains.
* Part II, Cholesterol Regulation of Ion Channels, examines the mechanisms underlying cholesterol sensitivities of ion channels, including the regulation of ion channels by cholesterol as a boundary lipid.
* Part III, Cholesterol Regulation of Receptors, explores the latest discoveries concerning how cholesterol regulates distinct types of receptors, including G-protein coupled receptors, LDL and scavenger receptors, and innate immune system receptors.
Increased levels of cholesterol represent a major health risk. Understanding cholesterol regulation of ion channels and receptors is essential for facilitating the development of new therapeutic strategies to alleviate the impact of pathological cholesterol conditions. With this book as their guide, readers have access to the most current knowledge in the field.
eBook
Membranes for gas separations
\"This book aims at illustrating several examples of different membrane compositions ranging from inorganic, polymeric, metallic, metal organic framework, and composite which have been successfully deployed to separate industrially relevant gas mixtures including hydrogen, nitrogen, methane, carbon dioxide, olefins/parafins among others. Each book chapter highlights some of the current and key fundamental and technological challenges for these membranes that must be overcome in order to envision its application at industrial level.\"--Page [4] of cover.
Book
Protein assemblies ejected directly from native membranes yield complexes for mass spectrometry
Insights into the architecture and stoichiometry of membrane complexes have grown with advances in cryo–electron microscopy and native mass spectroscopy. However, most of these studies are not in the context of native membrane. Chorev et al. released intact membrane complexes directly from native lipid membrane vesicles into a mass spectrometer. They analyzed components of the Escherichia coli inner and outer membranes and the bovine mitochondrial inner membrane. For several identified complexes, they found a stoichiometry that differs from published results and, in some cases, confirmed interactions that could not be characterized structurally. Science , this issue p. 829 Mass spectra reveal the composition of complexes ejected directly from native cellular membrane environments. Membrane proteins reside in lipid bilayers and are typically extracted from this environment for study, which often compromises their integrity. In this work, we ejected intact assemblies from membranes, without chemical disruption, and used mass spectrometry to define their composition. From Escherichia coli outer membranes, we identified a chaperone-porin association and lipid interactions in the β-barrel assembly machinery. We observed efflux pumps bridging inner and outer membranes, and from inner membranes we identified a pentameric pore of TonB, as well as the protein-conducting channel SecYEG in association with F 1 F O adenosine triphosphate (ATP) synthase. Intact mitochondrial membranes from Bos taurus yielded respiratory complexes and fatty acid–bound dimers of the ADP (adenosine diphosphate)/ATP translocase (ANT-1). These results highlight the importance of native membrane environments for retaining small-molecule binding, subunit interactions, and associated chaperones of the membrane proteome.
Journal Article
A new antibiotic traps lipopolysaccharide in its intermembrane transporter
Gram-negative bacteria are extraordinarily difficult to kill because their cytoplasmic membrane is surrounded by an outer membrane that blocks the entry of most antibiotics. The impenetrable nature of the outer membrane is due to the presence of a large, amphipathic glycolipid called lipopolysaccharide (LPS) in its outer leaflet
1
. Assembly of the outer membrane requires transport of LPS across a protein bridge that spans from the cytoplasmic membrane to the cell surface. Maintaining outer membrane integrity is essential for bacterial cell viability, and its disruption can increase susceptibility to other antibiotics
2
–
6
. Thus, inhibitors of the seven lipopolysaccharide transport (Lpt) proteins that form this transenvelope transporter have long been sought
7
–
9
. A new class of antibiotics that targets the LPS transport machine in
Acinetobacter
was recently identified. Here, using structural, biochemical and genetic approaches, we show that these antibiotics trap a substrate-bound conformation of the LPS transporter that stalls this machine. The inhibitors accomplish this by recognizing a composite binding site made up of both the Lpt transporter and its LPS substrate. Collectively, our findings identify an unusual mechanism of lipid transport inhibition, reveal a druggable conformation of the Lpt transporter and provide the foundation for extending this class of antibiotics to other Gram-negative pathogens.
A mechanism of lipid transport inhibition has been identified for a class of peptide antibiotics effective against resistant
Acinetobacter
strains, which may have applications in the inhibition of other Gram-negative pathogens.
Journal Article
New membranes and advanced materials for wastewater treatment
This volume reports state-of-the-art research on new membranes, e.g. innovative solutions to fouling. Additionally, as membrane processes produce higher water purity, concerns over lower concentration contaminants (e.g. hormones, drugs, metals, toxins, and other small moclecule contaminants) must be addressed. Several chapters describe the synthesis and use of molecularly imprinted polymers - exciting new materials that can selectively remove compounds at very low concentrations. A number of chapters describe innovative materials and processes for specific metal removal and concentration.
Book
How cholesterol stiffens unsaturated lipid membranes
Cholesterol is an integral component of eukaryotic cell membranes and a key molecule in controlling membrane fluidity, organization, and other physicochemical parameters. It also plays a regulatory function in antibiotic drug resistance and the immune response of cells against viruses, by stabilizing the membrane against structural damage. While it iswell understood that, structurally, cholesterol exhibits a densification effect on fluid lipid membranes, its effects on membrane bending rigidity are assumed to be nonuniversal; i.e., cholesterol stiffens saturated lipid membranes, but has no stiffening effect on membranes populated by unsaturated lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). This observation presents a clear challenge to structure–property relationships and to our understanding of cholesterol-mediated biological functions. Here, using a comprehensive approach—combining neutron spin-echo (NSE) spectroscopy, solid-state deuterium NMR (²H NMR) spectroscopy, and molecular dynamics (MD) simulations—we report that cholesterol locally increases the bending rigidity of DOPC membranes, similar to saturated membranes, by increasing the bilayer’s packing density. All three techniques, inherently sensitive to mesoscale bending fluctuations, show up to a threefold increase in effective bending rigidity with increasing cholesterol content approaching a mole fraction of 50%. Our observations are in good agreement with the known effects of cholesterol on the area-compressibility modulus and membrane structure, reaffirming membrane structure–property relationships. The current findings point to a scale-dependent manifestation of membrane properties, highlighting the need to reassess cholesterol’s role in controlling membrane bending rigidity over mesoscopic length and time scales of important biological functions, such as viral budding and lipid–protein interactions.
Journal Article
Lipid Rafts As a Membrane-Organizing Principle
Cell membranes display a tremendous complexity of lipids and proteins designed to perform the functions cells require. To coordinate these functions, the membrane is able to laterally segregate its constituents. This capability is based on dynamic liquid-liquid immiscibility and underlies the raft concept of membrane subcompartmentalization. Lipid rafts are fluctuating nanoscale assemblies of sphingolipid, cholesterol, and proteins that can be stabilized to coalesce, forming platforms that function in membrane signaling and trafficking. Here we review the evidence for how this principle combines the potential for sphingolipid-cholesterol self-assembly with protein specificity to selectively focus membrane bioactivity.
Journal Article