Basic cell penetrating peptides induce plasma membrane positive curvature, lipid domain separation and protein redistribution

International audienceBasic cell penetrating peptides are tools for molecular cellular internalization of non membrane permeable molecules. Their uptake mechanisms involve energy-dependent and energy-independent pathways such as endocytosis, direct translocation or physical endocytosis. These mechanisms are ruled by both, the peptides physicochemical properties and structure and by the membrane lipids characteristics and organisation. Herein we used plasma membrane spheres and membrane models to study the membrane perturbations induced by three arginine-rich cell penetrating peptides. Nona-arginine (R9) and the amphipathic peptide RWRRWWRRW (RW9) induced positive membrane curvature in the form of buds and membrane tubes. Membranous tubes underwent rolling resulting in formation of multilamellar membrane particles at the surface of the plasma membrane spheres. The amphipathic peptides RW9 and RRWRRWWRRWWRRWRR (RW16) provoked lipid and membrane associated protein domain separation as well as changes in membrane fluidity and cholesterol redistribution. These data suggest that membrane domains separation and the formation of multilamellar membranous particles would be involved in arginine-rich cell penetrating peptides internalization

Metabolic energy-independent mechanism of internalization for the cell penetrating peptide penetratin

International audienceCellular uptake of vector peptides used for internalization of hydrophilic molecules into cells is known to follow two different pathways: direct translocation of the plasma membrane and internalization by endocytosis followed by release into the cytosol. These pathways differ in their energy dependence. The first does not need metabolic energy while the second requires metabolic energy. Herein we used erythrocytes and plasma membrane vesicles to study membrane perturbations induced by the cell penetrating peptide penetratin. The results show that cell penetrating peptides are able to be internalized by two metabolic energy-independent pathways: direct crossing of the plasma membrane and endocytosis-like mechanisms. The last mechanism involves the induction of membrane negative curvature resulting in invaginations that mimic the endosomal uptake in the absence of ATP. This new mechanism called "physical endocytosis" or "self-induced endocytosis" might explain different data concerning the independence or dependence on metabolic energy during cellular uptake and reveals the autonomous capacity of peptides to induce their internalization. 2 Keywords: Membrane invagination/ metabolic energy/ penetratin/ penetrating peptide/ physical endocytosis/ self-induced endocytosis

Getting the farm to the school: Increasing direct, local procurement in Yolo County schools

Since 2012, the UC Sustainable Agriculture Research and Education Program (SAREP) has worked with the Yolo County Department of Agriculture to support farm to school activities in Yolo County. In 2015, SAREP partnered with the Yolo County Department of Agriculture to deepen engagement with Yolo County growers and increase direct sales to Yolo County schools. SAREP tracked the volumes and prices of produce purchased by five school districts for the 2014–2015 baseline year and the 2015–2016 school year. Analysis was completed for three school districts for common produce items purchased, increases in in-season purchasing and direct grower versus distributor sales. For these districts, 17 produce items were in the top 10 for at least one of the districts; the five most common were apples, bananas, lettuce, oranges and strawberries, four of which are available locally for some or all of the school year. Districts purchased between 50% and 75% of their produce in season by the end of year two. All districts increased their purchases directly from growers. Findings suggest how services for growers and school food buyers can contribute to more local procurement

Secondary structure of rhBMP-2 in a protective biopolymeric carrier material

Efficient delivery of growth factors is one of the great challenges of tissue engineering. Polyelectrolyte multilayer films (PEM) made of biopolymers have recently emerged as an interesting carrier for delivering recombinant human bone morphogenetic protein 2 (rhBMP-2 noted here BMP-2) to cells in a matrix-bound manner. We recently showed that PEM made of poly(l-lysine) and hyaluronan (PLL/HA) can retain high and tunable quantities of BMP-2 and can deliver it to cells to induce their differentiation in osteoblasts. Here, we investigate quantitatively by Fourier transform infrared spectroscopy (FTIR) the secondary structure of BMP-2 in solution as well as trapped in a biopolymeric thin film. We reveal that the major structural elements of BMP-2 in solution are intramolecular β-sheets and unordered structures as well as α-helices. Furthermore, we studied the secondary structure of rhBMP-2 trapped in hydrated films and in dry films since drying is an important step for future applications of these bioactive films onto orthopedic biomaterials. We demonstrate that the structural elements were preserved when BMP-2 was trapped in the biopolymeric film in hydrated conditions and, to a lesser extent, in dry state. Importantly, its bioactivity was maintained after drying of the film. Our results appear highly promising for future applications of these films as coatings of biomedical materials, to deliver bioactive proteins while preserving their bioactivity upon storage in dry state.This work was supported by the French Ministry of Research through an ANR-EmergenceBIO grant (ANR-09-EBIO-012-01), by the European Commission (FP7 program) via a European Research Council starting grant (BIOMIM, GA 259370), and by GRAVIT (081012_FIBIOS). C.P. is grafetul to IUF for financial support

Structure-Function Relations in Oxaloacetate Decarboxylase Complex. Fluorescence and Infrared Approaches to Monitor Oxomalonate and Na+ Binding Effect

ions across the membrane, which drives endergonic membrane reactions such as ATP synthesis, transport and motility. OAD is a membrane-bound enzyme composed of α, β and γ subunits. The α subunit contains the carboxyltransferase catalytic site. characteristic of a high content of α helix structures. Addition of oxomalonate induced a shift of the amide-I band of OAD toward higher wavenumbers, interpreted as a slight decrease of β sheet structures and a concomitant increase of α helix structures. Oxomalonate binding to αγand α subunits also provoked secondary structure variations, but these effects were negligible compared to OAD complex. alters the tryptophan environment of the β subunit, consistent with the function of these subunits within the enzyme complex. Formation of a complex between OAD and its substrates elicits structural changes in the α-helical as well as β-strand secondary structure elements

Distinct Behaviour of the Homeodomain Derived Cell Penetrating Peptide Penetratin in Interaction with Different Phospholipids

Penetratin is a protein transduction domain derived from the homeoprotein Antennapedia. Thereby it is currently used as a cell penetrating peptide to introduce diverse molecules into eukaryotic cells, and it could also be involved in the cellular export of transcription factors. Moreover, it has been shown that it is able to act as an antimicrobial agent. The mechanisms involved in all these processes are quite controversial.In this article, we report spectroscopic, calorimetric and biochemical data on the penetratin interaction with three different phospholipids: phosphatidylcholine (PC) and phosphatidylethanolamine (PE) to mimic respectively the outer and the inner leaflets of the eukaryotic plasma membrane and phosphatidylglycerol (PG) to mimic the bacterial membrane. We demonstrate that with PC, penetratin is able to form vesicle aggregates with no major change in membrane fluidity and presents no well defined secondary structure organization. With PE, penetratin aggregates vesicles, increases membrane rigidity and acquires an α-helical structure. With PG membranes, penetratin does not aggregate vesicles but decreases membrane fluidity and acquires a structure with both α-helical and β–sheet contributions.These data from membrane models suggest that the different penetratin actions in eukaryotic cells (membrane translocation during export and import) and on prokaryotes may result from different peptide and lipid structural arrangements. The data suggest that, for eukaryotic cell penetration, penetratin does not acquire classical secondary structure but requires a different conformation compared to that in solution

Coupling changes in cell shape to chromosome segregation

Animal cells undergo dramatic changes in shape, mechanics and polarity as they progress through the different stages of cell division. These changes begin at mitotic entry, with cell–substrate adhesion remodelling, assembly of a cortical actomyosin network and osmotic swelling, which together enable cells to adopt a near spherical form even when growing in a crowded tissue environment. These shape changes, which probably aid spindle assembly and positioning, are then reversed at mitotic exit to restore the interphase cell morphology. Here, we discuss the dynamics, regulation and function of these processes, and how cell shape changes and sister chromatid segregation are coupled to ensure that the daughter cells generated through division receive their fair inheritance

Structure of the complex of cytochrome c with cardiolipin in non-polar environment

The complex of mitochondrial protein cytochrome c (CytC) with anionic phospholipid cardiolipin (CL) plays a crucial role in the initiation of apoptosis by catalyzing lipid peroxidation in mitochondrial membranes. In our previous papers, we found that CytC and CL mixed in millimolar concentrations form a sediment showing microcrystals composed of nanospheres (Cyt-CL) of 11–12 and 8 nm in diameter. The hypothesis was proposed that Cyt-CL, having hydrophobic shell, may appear inside the membrane lipid bilayer in mitochondria and peroxidase membrane phospholipids so initiating the apoptotic cascade. In this work, Cyt-CL complex dissolved in chloroform or hexane was investigated as a model of the complex in mitochondrial membranes. We used dynamic light scattering method to measure the size of the particles. The analysis of particles size distribution of Cyt-CL in chloroform allows to reveal three dominant diameters of 12.1 ± 1.4, 7.8 ± 1.0, and 4.7 ± 0.7 nm. The first two values are closed to those, earlier obtained with small-angle X-ray scattering method in Cyt-CL microcrystals, 11.1 ± 1.0 and 8.0 ± 0.7 nm. CL extracted in chloroform-methanol forms a real solution of particles with diameter of 0.7 ± 0.1 nm. In methanol-water phase, CL and CL + CytC mixture form particles of 83.7 ± 9.8 and 71.3 ± 11.6 nm, respectively. Apparently, cardiolipin in 50% methanol forms single-layer liposomes regardless of the presence of CytC in the medium. Partial unfolding of CytC in the complex was evidenced by (a) appearance of fluorescence of tyrosine and tryptophan residues and (b) disappearance of the absorption band at 699 nm due to breakdown of heme iron – methionine bond > F⋯S(Met80). In hydrophobic solvent Cyt-CL exhibited quasi-lipoperoxidase and lipoxygenase activity as was shown in kinetic measurements of chemiluminescence enhanced by coumarin C-525, a selective sensitizer of chemiluminescence, associated with reactions of lipid peroxyl radicals. Our data in this model system do not contradict the hypothesis (Vladimirov, Y.A. et al. Biochemistry (Mosc) 78, 1086–1097) that nanospheres of Cyt-CL complex, embedded into the lipid phase of mitochondrial membrane, catalyze lipid peroxidation, thereby initiating apoptosis

Mechanisms bywhich dietary fatty acids regulate mitochondrial structure-function in health and disease

Mitochondria are the energy-producing organelles within a cell. Furthermore, mitochondria have a role in maintaining cellular homeostasis and proper calcium concentrations, building critical components of hormones and other signaling molecules, and controlling apoptosis. Structurally, mitochondria are unique because they have 2 membranes that allow for compartmentalization. The composition and molecular organization of thesemembranes are crucial to the maintenance and function of mitochondria. In this review, we first present a general overview of mitochondrial membrane biochemistry and biophysics followed by the role of different dietary saturated and unsaturated fatty acids in modulatingmitochondrial membrane structure-function.We focus extensively on long-chain n-3 (ω-3) polyunsaturated fatty acids and their underlyingmechanisms of action. Finally,we discuss implications of understanding molecular mechanisms by which dietary n-3 fatty acids targetmitochondrial structure-function in metabolic diseases such as obesity, cardiac-ischemia reperfusion injury, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and select cancers

Why Do Tethered-Bilayer Lipid Membranes Suit for Functional Membrane Protein Reincorporation?

Membrane proteins (MPs) are essential for cellular functions. Understanding the functions of MPs is crucial as they constitute an important class of drug targets. However, MPs are a challenging class of biomolecules to analyze because they cannot be studied outside their native environment. Their structure, function and activity are highly dependent on the local lipid environment, and these properties are compromised when the protein does not reside in the cell membrane. Mammalian cell membranes are complex and composed of different lipid species. Model membranes have been developed to provide an adequate environment to envisage MP reconstitution. Among them, tethered-Bilayer Lipid Membranes (tBLMs) appear as the best model because they allow the lipid bilayer to be decoupled from the support. Thus, they provide a sufficient aqueous space to envisage the proper accommodation of large extra-membranous domains of MPs, extending outside. Additionally, as the bilayer remains attached to tethers covalently fixed to the solid support, they can be investigated by a wide variety of surface-sensitive analytical techniques. This review provides an overview of the different approaches developed over the last two decades to achieve sophisticated tBLMs, with a more and more complex lipid composition and adapted for functional MP reconstitution