Ange Polidori

A class of mild surfactants that keep integral membrane proteins water-soluble for functional studies and crystallization

Abstract Mixed protein-surfactant micelles are used for in vitro studies and 3D crystallization when solutions of pure, monodisperse integral membrane proteins are required. However, many membrane proteins undergo inactivation when transferred from the biomembrane into micelles of conventional surfactants with alkyl chains as hydrophobic moieties. Here we describe the development of surfactants with rigid, saturated or aromatic hydrocarbon groups as hydrophobic parts. Their stabilizing properties are demonstrated with three different integral membrane proteins. The temperature at which 50% of the binding sites for specific ligands are lost is used as a measure of stability and dodecyl-β-D-maltoside (‘C12-b-M’) as a reference for conventional surfactants. One surfactant increased the stability of two different G protein-coupled receptors and the human Patched protein receptor by approximately 10°C compared to C12-b-M. Another surfactant yielded the highest stabilization of the human Patched protein receptor compared to C12-b-M (13°C) but was inferior for the G protein-coupled receptors. In addition, one of the surfactants was successfully used to stabilize and crystallize the cytochrome b6 f complex from Chlamydomonas reinhardtii. The structure was solved to the same resolution as previously reported in C12-b-M.

Synthesis and preliminary biological studies of hemifluorinated bifunctional bolaamphiphiles designed for gene delivery

The multistep synthesis of a new series of dissymmetric hemifluorocarbon bolaamphiphiles designed for gene transport is described. The dissymmetric functionalization of diiodoperfluoroctane leads to bolaamphiphile molecules composed of a partially fluorocarbon core end-capped with a glycoside and an ammonium salt derived from histidine or lysine. Initial biological results indicate that one of the bolaamphiphile—end-capped with a lysine and a lactobionamide residue—induces a remarkably low cytotoxicity on COS-7 cells and, when self-assembled with DNA plasmid, generates a significant in vitro transfection efficiency without the addition of any fusogenic lipid.

Mitochondrial medicine: neuroprotection and life extension by the new amphiphilic nitrone LPBNAH1 acting as a highly potent antioxidant agent

The search for effective treatments that prevent oxidative stress associated with premature ageing and neurodegenerative diseases is an important area of neurochemical research. As age‐ and disease‐related oxidative stress is frequently associated with mitochondrial dysfunction, amphiphilic antioxidant agents of high stability and selectivity that target these organelles can provide on‐site protection. Such an amphiphilic nitrone protected human neuroblastoma cells at low micromolar concentrations against oxidative damage and death induced by exposure to the β‐amyloid peptide, hydrogen peroxide and 3‐hydroxykynurenine. Daily administration of the antioxidant at a concentration of only 5 μm significantly increased the lifespan of the individually cultured rotifer Philodina acuticornis odiosa Milne. This compound is unique in its exceptional anti‐ageing efficacy, being one order of magnitude more potent than any other compound previously tested on rotifers. The nitrone protected these aquatic animals against the lethal toxicity of hydrogen peroxide and doxorubicin and greatly enhanced their survival when co‐administered with these oxidotoxins. These findings indicate that amphiphilic antioxidants have a great potential as neuroprotective agents in preventing the death of cells and organisms exposed to enhanced oxidative stress and damage.

Drug Delivery Systems Using Immobilized Intact Liposomes: A Comparative and Critical Review

Liposomes sustain considerable interest to develop ways to fabricate drug delivery systems that would provide a good release without inducing any systemic reactions into the host. However, in many cases, liposomes injected into the blood stream are rapidly cleared from the system and only a fraction reaches the target site even when poly(ethylene glycol) (PEG)-coated liposomes are used. Composite drug delivery systems with liposomes i.e., liposomes linked to other substrates can be good candidates for certain type of drug release to achieve a localised treatment. This paper reviews the fundamental phenomena of the interactions between liposomes and solid substrates. Then, we address various techniques that have been used to immobilize intact liposomes onto and into different substrates. Finally, properties of liposomes used as drug delivery systems are briefly reviewed.

Production of UCP1 a membrane protein from the inner mitochondrial membrane using the cell free expression system in the presence of a fluorinated surfactant

Structural studies of membrane protein are still challenging due to several severe bottlenecks, the first being the overproduction of well-folded proteins. Several expression systems are often explored in parallel to fulfil this task, or alternately prokaryotic analogues are considered. Although, mitochondrial carriers play key roles in several metabolic pathways, only the structure of the ADP/ATP carrier purified from bovine heart mitochondria was determined so far. More generally, characterisations at the molecular level are restricted to ADP/ATP carrier or the uncoupling protein UCP1, another member of the mitochondrial carrier family, which is abundant in brown adipose tissues. Indeed, mitochondrial carriers have no prokaryotic homologues and very few efficient expression systems were described so far for these proteins. We succeeded in producing UCP1 using a cell free expression system based on E. coli extracts, in quantities that are compatible with structural approaches. The protein was synthesised in the presence of a fluorinated surfactant, which maintains the protein in a soluble form. Further biochemical and biophysical analysis such as size exclusion chromatography, circular dichroism and thermal stability, of the purified protein showed that the protein is non-aggregated, monodisperse and well-folded.

Synthesis of a new family of glycolipidic nitrones as potential antioxidant drugs for neurodegenerative disorders.

This paper deals with the synthesis of a novel series of amphiphilic glycosylated spin-traps derived from alpha-Phenyl-N-tert-butyl nitrone (PBN) and an initial characterization of their anti-caspase-3 activity. Preliminary investigation of their anti-apoptosis effect showed they dramatically inhibit the activity of caspase-3 in cultured neuronal cells following induction of apoptosis by hydrogen peroxide.

Vesicles and other supramolecular systems made from double-tailed synthetic glycolipids derived from galactosylated tris(hydroxymethyl)aminomethane

Abstract A series of double-tailed hydrocarbon glycolipids derived from tris(hydroxymethyl)aminomethane (Tris) have been prepared. These amphiphiles consist of three parts: a hydrophilic head derived from mono- or polygalactosylated Tris, a linking arm of peptidic nature and a hydrophobic double tail composed of 12 or 18 carbon atom chains. The ability of the new glycolipids to disperse in water, the morphology of the self-assemblies they form and the stability of the latter were shown to depend largely on the volumetric ratio between hydrophilic head and hydrophobic tails. Comparative studies of such substrates allowed a better understanding of the relative role of the various parameters that govern the formation of tubular systems relative to vesicular organizations. In all cases, the introduction of oligomeric galactosylated heads favoured stable vesicular systems over tubules.

Amphipol-mediated screening of molecular orthoses specific for membrane protein targets.

Specific, tight-binding protein partners are valuable helpers to facilitate membrane protein (MP) crystallization, because they can i) stabilize the protein, ii) reduce its conformational heterogeneity, and iii) increase the polar surface from which well-ordered crystals can grow. The design and production of a new family of synthetic scaffolds (dubbed αReps, for “artificial alpha repeat protein”) have been recently described. The stabilization and immobilization of MPs in a functional state are an absolute prerequisite for the screening of binders that recognize specifically their native conformation. We present here a general procedure for the selection of αReps specific of any MP. It relies on the use of biotinylated amphipols, which act as a universal “Velcro” to stabilize, and immobilize MP targets onto streptavidin-coated solid supports, thus doing away with the need to tag the protein itself.

Amphiphilic Amide Nitrones: A New Class of Protective Agents Acting as Modifiers of Mitochondrial Metabolism

Our group has demonstrated that the amphiphilic character of alpha-phenyl-N-tert-butyl nitrone based agents is a key feature in determining their bioactivity and protection against oxidative toxicity. In this work, we report the synthesis of a new class of amphiphilic amide nitrones. Their hydroxyl radical scavenging activity and radical reducing potency were shown using ABTS competition and ABTS(+) reduction assays, respectively. Cyclic voltammetry was used to investigate their redox behavior, and the effects of the substitution of the PBN on the charge density of the nitronyl atoms, the electron affinity, and the ionization potential were computationally rationalized. The protective effects of amphiphilic amide nitrones in cell cultures exposed to oxidotoxins greatly exceeded those exerted by the parent compound PBN. They decreased electron and proton leakage as well as hydrogen peroxide formation in isolated rat brain mitochondria at nanomolar concentration. They also significantly enhanced mitochondrial membrane potential. Finally, dopamine-induced inhibition of complex I activity was antagonized by pretreatment with these agents. These findings indicate that amphiphilic amide nitrones are much more than just radical scavenging antioxidants but may act as a new class of bioenergetic agents directly on mitochondrial electron and proton transport.

Stability study of the human G-protein coupled receptor, Smoothened.

Smoothened is a member of the G-protein coupled receptor (GPCR) family responsible for the transduction of the Hedgehog signal to the intracellular effectors of the Hedgehog signaling pathway. Aberrant regulation of this receptor is implicated in many cancers but also in neurodegenerative disorders. Despite the pharmacological relevance of this receptor, very little is known about its functional mechanism and its physiological ligand. In order to characterize this receptor for basic and pharmacological interests, we developed the expression of human Smoothened in the yeast Saccharomyces cerevisiae and Smoothened was then purified. Using Surface Plasmon Resonance technology, we showed that human Smoothened was in a native conformational state and able to interact with its antagonist, the cyclopamine, both at the yeast plasma membrane and after purification. Thermostability assays on purified human Smoothened showed that this GPCR is relatively stable in the classical detergent dodecyl-beta-d-maltoside (DDM). The fluorinated surfactant C(8)F(17)TAC, which has been proposed to be less aggressive towards membrane proteins than classical detergents, increased Smoothened thermostability in solution. Moreover, the replacement of a glycine by an arginine in the third intracellular loop of Smoothened coupled to the use of the fluorinated surfactant C(8)F(17)TAC during the mutant purification increased Smoothened thermostability even more. These data will be very useful for future crystallization assays and structural characterization of the human receptor Smoothened.