Functioning and processing of membrane proteins critically depend on the way their transmembrane segments are embedded in the membrane. Sphingolipids are structural components of membranes and can ...also act as intracellular second messengers. Not much is known of sphingolipids binding to transmembrane domains (TMDs) of proteins within the hydrophobic bilayer, and how this could affect protein function. Here we show a direct and highly specific interaction of exclusively one sphingomyelin species, SM 18, with the TMD of the COPI machinery protein p24 (ref. 2). Strikingly, the interaction depends on both the headgroup and the backbone of the sphingolipid, and on a signature sequence (VXXTLXXIY) within the TMD. Molecular dynamics simulations show a close interaction of SM 18 with the TMD. We suggest a role of SM 18 in regulating the equilibrium between an inactive monomeric and an active oligomeric state of the p24 protein, which in turn regulates COPI-dependent transport. Bioinformatic analyses predict that the signature sequence represents a conserved sphingolipid-binding cavity in a variety of mammalian membrane proteins. Thus, in addition to a function as second messengers, sphingolipids can act as cofactors to regulate the function of transmembrane proteins. Our discovery of an unprecedented specificity of interaction of a TMD with an individual sphingolipid species adds to our understanding of why biological membranes are assembled from such a large variety of different lipids.
This paper reviews the current knowledge on the various mechanisms for transbilayer, or flip-flop, lipid motion in model and cell membranes, enzyme-assisted lipid transfer by flippases, floppases and ...scramblases is briefly discussed, while non-catalyzed lipid flip-flop is reviewed in more detail. Transbilayer lipid motion may occur as a result of the insertion of foreign molecules (detergents, lipids, or even proteins) in one of the membrane leaflets. It may also be the result of the enzymatic generation of lipids, e.g. diacylglycerol or ceramide, at one side of the membrane. Transbilayer motion rates decrease in the order diacylglycerol
≫
ceramide
≫
phospholipids. Ceramide, but not diacylglycerol, can induce transbilayer motion of other lipids, and bilayer scrambling. Transbilayer lipid diffusion and bilayer scrambling are defined as two conceptually and mechanistically different processes. The mechanism of scrambling appears to be related to local instabilities caused by the non-lamellar ceramide molecule, or by other molecules that exhibit a relatively slow flip-flop rate, when asymmetrically inserted or generated in one of the monolayers in a cell or model membrane.
Cellular membranes are fundamental building blocks regulating an extensive repertoire of biological functions. These structures contain lipids and membrane proteins that are known to laterally ...self-aggregate in the plane of the membrane, forming defined membrane nanoscale domains essential for protein activity. Membrane rafts are described as heterogeneous, dynamic, and short-lived cholesterol- and sphingolipid-enriched membrane nanodomains (10–200 nm) induced by lipid-protein and lipid-lipid interactions. Those membrane nanodomains have been extensively characterized using model membranes and in silico methods. However, despite the development of advanced fluorescence microscopy techniques, undoubted nanoscale visualization by imaging techniques of membrane rafts in the membrane of unperturbed living cells is still uncompleted, increasing the skepticism about their existence. Here, we broadly review recent biochemical and microscopy techniques used to investigate membrane rafts in living cells and we enumerate persistent open questions to answer before unlocking the mystery of membrane rafts in living cells.
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•Lipid rafts existence in living unperturbed cells is still not fully solved.•Different strategies can be used for visualizing lipid nanodomains in living cells.•Super-resolution microscopy techniques are key techniques to visualize lipid rafts.•Novel membranes probes suitable for super-resolution microscopy are required for membrane research
Metastasis is the leading cause of cancer-related deaths, and greater knowledge of the metastatic microenvironment is necessary to effectively target this process. Microenvironmental changes occur at ...distant sites prior to clinically detectable metastatic disease; however, the key niche regulatory signals during metastatic progression remain poorly characterized. Here, we identify a core immune suppression gene signature in pre-metastatic niche formation that is expressed predominantly by myeloid cells. We target this immune suppression program by utilizing genetically engineered myeloid cells (GEMys) to deliver IL-12 to modulate the metastatic microenvironment. Our data demonstrate that IL12-GEMy treatment reverses immune suppression in the pre-metastatic niche by activating antigen presentation and T cell activation, resulting in reduced metastatic and primary tumor burden and improved survival of tumor-bearing mice. We demonstrate that IL12-GEMys can functionally modulate the core program of immune suppression in the pre-metastatic niche to successfully rebalance the dysregulated metastatic microenvironment in cancer.
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•A myeloid-rich, T-cell-poor immunosuppressive microenvironment promotes metastasis•Genetically engineered myeloid cells (GEMys) deliver IL-12 to metastatic sites•IL12-GEMys reverse immune suppression and activate anti-tumor immunity•Chemotherapy with IL12-GEMy treatment achieves durable cures in pre-clinical models
Genetically engineered myeloid cells expressing IL-12 can reverse the immunosuppressive environment developed during metastatic progression by augmenting T cell responses and reducing metastatic burden in preclinical models.
We present a combined atomic force microscopy and fluorescence microscopy study of the behavior of a ternary supported lipid bilayer system containing a saturated lipid (DPPC), an unsaturated lipid ...(DOPC), and ergosterol in the presence of high ethanol (20 vol %). We find that the fluorescent probe Texas Red DHPE preferentially partitions into the ethanol-induced interdigitated phase, which allows the use of fluorescence imaging to investigate the phase behavior of the system. Atomic force microscopy and fluorescence images of samples with the same lipid mixture show good agreement in sample morphology and area fractions of the observed phases. Using area fractions obtained from fluorescence images over a broad range of compositions, we constructed a phase diagram of the DPPC/DOPC/ergosterol system at 20 vol % ethanol. The phase diagram clearly shows that increasing unsaturated lipid and/or ergosterol protects the membrane by preventing the formation of the interdigitated phase. This result supports the hypothesis that yeast cells increase ergosterol and unsaturated lipid content to prevent interdigitation and maintain an optimal membrane thickness as ethanol concentration increases during anaerobic fermentations. Changes in plasma membrane composition provide an important survival factor for yeast cells to deter ethanol toxicity.
The voltage-dependent motor protein prestin (also known as SLC26A5) is responsible for the electromotive behaviour of outer-hair cells and underlies the cochlear amplifier
. Knockout or impairment of ...prestin causes severe hearing loss
. Despite the key role of prestin in hearing, the mechanism by which mammalian prestin senses voltage and transduces it into cellular-scale movements (electromotility) is poorly understood. Here we determined the structure of dolphin prestin in six distinct states using single-particle cryo-electron microscopy. Our structural and functional data suggest that prestin adopts a unique and complex set of states, tunable by the identity of bound anions (Cl
or SO
). Salicylate, a drug that can cause reversible hearing loss, competes for the anion-binding site of prestin, and inhibits its function by immobilizing prestin in a new conformation. Our data suggest that the bound anion together with its coordinating charged residues and helical dipole act as a dynamic voltage sensor. An analysis of all of the anion-dependent conformations reveals how structural rearrangements in the voltage sensor are coupled to conformational transitions at the protein-membrane interface, suggesting a previously undescribed mechanism of area expansion. Visualization of the electromotility cycle of prestin distinguishes the protein from the closely related SLC26 anion transporters, highlighting the basis for evolutionary specialization of the mammalian cochlear amplifier at a high resolution.
The objective of the present study was to determine the effectiveness of a 6-week balance training program on patients with Chronic Ankle Instability (CAI) in relation to the results obtained in ...Dynamic Balance, subjective feeling of instability and pain using a single-blind randomized controlled trial. 70 athletes were randomly assigned to control or intervention group. The control group performed their usual training, and the intervention group was administered the same usual activity in addition to a balance program. The paired t-test was performed to evaluate the change scores in each group. The t-test for independent samples was performed to evaluate between-group differences in change scores. Significance level was assigned for p-values less than 0.05 for all analyses. There were significant differences between groups in change scores in CAIT and all of the SEBTs reach distances (p<0.001) but not in Pain (p=0.586). The effect sizes were larger for the outcomes measures that showed significant differences. In the within-group change, the experimental groups showed larger effect sizes in CAIT, SEBT posteromedial and SEBT posterolateral, and moderate effect sizes in SEBT anterior. Exercise therapy training based on multi-station balance tasks led to significant improvements in dynamic balance and self-reported sensation of instability in patients with CAI.
The COVID-19 pandemic has been recognized as a trigger for redefining supply chains at the global level, and has created an intense debate within the academic community and among policy-makers and ...practitioners. Among other industries, health care has been dramatically hit by the scarcity of "medical products," specifically for personal protective equipment (PPE-like), due to supply chain disruptions coupled with dramatically increased demand. We aimed to analyze how the scarcity of PPE-like during the COVID-19 pandemic has modified the behavior of decision-makers in the PPE-like supply chain at the hospital level, and to explore what changes could be implemented to cope with future PPE-like shortages.
We used an explorative approach based on semi-structured interviews with key informants in the Spanish health care industry. More specifically, we held interviews to industry experts at three hospitals in three Spanish regions to map the consequences of the COVID-19 pandemic onto the buying decision-making process.
Different strategies were developed by decision-makers at hospitals before, during, and after the first wave of the COVID-19 pandemic in Spain. Our paper offers two main findings: a) decision-makers changed their purchasing behavior from a cost main driver to guaranteeing the availability of supplies; b) they supported the idea of giving more "strategic autonomy" to Spain or Europe through back and nearshoring decisions.
This paper could be of interest to health care management at the national, regional, and hospital levels, as well as for policy-makers, since it could help to establish and configure policies to support the sourcing of medical products (specifically PPE-like) to anticipate potential supply disruptions. Our paper contributes to the limited existing literature on how purchasing strategies at the decision-maker level and supply vary in the health care industry when a public health crisis appears, and what potential solutions might be for policy-makers and practitioners involved in the health care industry.
Mislabeling of seafood is a global phenomenon that can misrepresent the status and level of consumption of wild fish stocks while concealing the use of many other wild species or those originating ...from aquaculture and sold as substitutes. We conducted a DNA barcoding study in three cities within Mexico (Mazatlan, Mexico City and Cancun) and sequenced the COI gene in 376 fish samples sold as 48 distinct commercial names at fish markets, grocery stores, and restaurants. Our goal was to identify the main species sold, their mislabeling rates and the species most used as substitutes. Overall, the study-wide mislabeling rate was 30.8% (95% CI 26.4-35.6). Half of the samples collected belonged to five species traded globally (yellowfin tuna, Atlantic salmon, mahi, swai, and tilapia), most of them with important aquaculture or ranching production levels. These species were commonly used as substitutes for other species and showed low mislabeling rates themselves (≤ 11%, except mahi mahi with 39% mislabeling). The other half of the samples revealed nearly 100 species targeted by small-scale fishers in Mexico and sold under 42 distinct commercial names. Popular local commercial names (dorado, marlin, mero, robalo, mojarra, huachinango, pargo, sierra) showed the highest mislabeling rates (36.3% to 94.4%) and served to sell many of the 53 species identified as substitutes in our study. We discuss the observed patterns in relation to landing and import data showing differences in availability of commercial species and the links to explain observed mislabeling rates and the use of a species as a substitute for other species. We also outline some of the implications of establishing a labeling and traceability standard as an alternative to improve transparency in the trade of seafood products in Mexico.
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