22 research outputs found
Corrigendum to “The dynamics of giant unilamellar vesicle oxidation probed by morphological transitions” [Biochim. Biophys. Acta 1838 (2014) 2615–2624]
Permeability of DOPC bilayers under photoinduced oxidation: Sensitivity to photosensitizer.
The modification of lipid bilayer permeability is one of the most striking yet poorly understood physical transformations that follow photoinduced lipid oxidation. We have recently proposed that the increase of permeability of photooxidized 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers is controlled by the time required by the oxidized lipid species to diffuse and aggregate into pores. Here we further probe this mechanism by studying photosensitization of DOPC membranes by methylene blue (MB) and DO15, a more hydrophobic phenothiazinium photosensitizer, under different irradiation powers. Our results not only reveal the interplay between the production rate and the diffusion of the oxidized lipids, but highlight also the importance of photosensitizer localization in the kinetics of oxidized membrane permeability
Oxidation of Membrane Curvature-Regulating Phosphatidylethanolamine Lipid Results in Formation of Bilayer and Cubic Structures
Oxidation
is associated with conditions related to chronic inflammations
and aging. Cubic structures have been observed in the smooth endoplasmic
reticulum and mitochondrial membranes of cells under oxidative stress
(e.g., tumor cells and virus-infected cells). It has been previously
suspected that oxidation can result in the rearrangement of lipids
from a fluid lamellar phase to a cubic structure in organelles containing
membranes enriched with amphiphiles that have nonzero intrinsic curvature,
such as phosphatidylethanolamine (PE) and cardiolipin. This study
focuses on the oxidation of 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphoethanolamine
(DOPE), a lipid that natively forms an inverted hexagonal phase at
physiological conditions. The oxidized samples contain an approximately
3:2 molar ratio of nonoxidized to oxidized DOPE. Optical microscopy
images collected during the hydration of this mixture from a dried
film suggest that the system evolves into a coexistence of a stable
fluid lamellar phase and transient square lattice structures with
unit cell sizes of 500–600 nm. Small-angle X-ray scattering
of the same lipid mixture yielded a body-centered Im3m cubic phase
with the lattice parameter of 14.04 nm. On average, the effective
packing parameter of the oxidized DOPE species was estimated to be
0.657 ± 0.069 (standard deviation). This suggests that the oxidation
of PE leads to a group of species with inverted molecular intrinsic
curvature. Oxidation can create amphiphilic subpopulations that potently
impact the integrity of the membrane, since negative Gaussian curvature
intrinsic to cubic phases can enable membrane destabilization processes
Corrigendum to “The dynamics of giant unilamellar vesicle oxidation probed by morphological transitions” [Biochim. Biophys. Acta 1838 (2014) 2615–2624]
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Membrane Curvature-sensing and Curvature-inducing Activity of Islet Amyloid Polypeptide and Its Implications for Membrane Disruption.
Islet amyloid polypeptide (IAPP) is a 37-amino acid amyloid protein intimately associated with pancreatic islet β-cell dysfunction and death in type II diabetes. In this study, we combine spectroscopic methods and microscopy to investigate α-helical IAPP-membrane interactions. Using light scattering and fluorescence microscopy, we observe that larger vesicles become smaller upon treatment with human or rat IAPP. Electron microscopy shows the formation of various highly curved structures such as tubules or smaller vesicles in a membrane-remodeling process, and spectrofluorometric detection of vesicle leakage shows disruption of membrane integrity. This effect is stronger for human IAPP than for the less toxic rat IAPP. From CD spectra in the presence of different-sized vesicles, we also uncover the membrane curvature-sensing ability of IAPP and find that it transitions from inducing to sensing membrane curvature when lipid negative charge is decreased. Our in vivo EM images of immunogold-labeled rat IAPP and human IAPP show both forms to localize to mitochondrial cristae, which contain not only locally curved membranes but also phosphatidylethanolamine and cardiolipin, lipids with high spontaneous negative curvature. Disruption of membrane integrity by induction of membrane curvature could apply more broadly to other amyloid proteins and be responsible for membrane damage observed in other amyloid diseases as well
Thiol–Ene Chemistry: A Greener Approach to Making Chemically and Thermally Stable Fibers
Fibers of micrometer and submicrometer diameters have been of significant interest in recent years owing to their advanced applications in diverse fields such as optoelectronics, regenerative medicine, piezoelectrics, ceramic materials, etc. There are a number of processes to make thin fibers including electrospinning, melt blowing, and recently developed Forcespinning. However, use of solvents or heat to lower viscosity for processing is common to all existing polymer fiber manufacturing methods, and a greener approach to making fibers remains a challenge. Interestingly, nature has engineered spiders and silkworms with a benign way of making mechanically strong and tough fibers through an intricate self-assembly of protein constituents during the fiber formation process. Comprehending the biosynthetic process and precisely replicating it has been a challenging task. However, we find that extruding small functional segments into solid fibrillar structures, through mediation of chemical interactions between the subunits, is a design approach that can be broadly adapted from nature to realize a greener fiber manufacturing process. Using the robust chemistry of thiol–ene photopolymerization, we demonstrate here that a photocurable mixture of a multifunctional acrylate, a tetrafunctional thiol, and a photoinitiator can be processed into continuous fibers by <i>in situ</i> photopolymerization during electrospinning under ambient conditions. The fibers are mechanically robust and have excellent chemical and thermal stability. While electrospinning has been used to demonstrate this concept, the chemistry could be broadly adapted into other fiber manufacturing methods to produce fibers without using solvents or heat
Membrane Curvature-sensing and Curvature-inducing Activity of Islet Amyloid Polypeptide and Its Implications for Membrane Disruption.
Islet amyloid polypeptide (IAPP) is a 37-amino acid amyloid protein intimately associated with pancreatic islet β-cell dysfunction and death in type II diabetes. In this study, we combine spectroscopic methods and microscopy to investigate α-helical IAPP-membrane interactions. Using light scattering and fluorescence microscopy, we observe that larger vesicles become smaller upon treatment with human or rat IAPP. Electron microscopy shows the formation of various highly curved structures such as tubules or smaller vesicles in a membrane-remodeling process, and spectrofluorometric detection of vesicle leakage shows disruption of membrane integrity. This effect is stronger for human IAPP than for the less toxic rat IAPP. From CD spectra in the presence of different-sized vesicles, we also uncover the membrane curvature-sensing ability of IAPP and find that it transitions from inducing to sensing membrane curvature when lipid negative charge is decreased. Our in vivo EM images of immunogold-labeled rat IAPP and human IAPP show both forms to localize to mitochondrial cristae, which contain not only locally curved membranes but also phosphatidylethanolamine and cardiolipin, lipids with high spontaneous negative curvature. Disruption of membrane integrity by induction of membrane curvature could apply more broadly to other amyloid proteins and be responsible for membrane damage observed in other amyloid diseases as well
Media 1: Optical stretching of giant unilamellar vesicles with an integrated dual-beam optical trap
Originally published in Biomedical Optics Express on 01 October 2012 (boe-3-10-2419