Active Fragments from Pro- and Antiapoptotic BCL-2 Proteins Have Distinct Membrane Behavior Reflecting Their Functional Divergence

BACKGROUND: The BCL-2 family of proteins includes pro- and antiapoptotic members acting by controlling the permeabilization of mitochondria. Although the association of these proteins with the outer mitochondrial membrane is crucial for their function, little is known about the characteristics of this interaction. METHODOLOGY/PRINCIPAL FINDINGS: Here, we followed a reductionist approach to clarify to what extent membrane-active regions of homologous BCL-2 family proteins contribute to their functional divergence. Using isolated mitochondria as well as model lipid Langmuir monolayers coupled with Brewster Angle Microscopy, we explored systematically and comparatively the membrane activity and membrane-peptide interactions of fragments derived from the central helical hairpin of BAX, BCL-xL and BID. The results show a connection between the differing abilities of the assayed peptide fragments to contact, insert, destabilize and porate membranes and the activity of their cognate proteins in programmed cell death. CONCLUSION/SIGNIFICANCE: BCL-2 family-derived pore-forming helices thus represent structurally analogous, but functionally dissimilar membrane domains

Quantitative atomic force microscopy provides new insight into matrix vesicle mineralization

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Enzymes immobilized in Langmuir-Blodgett films: Why determining the surface properties in Langmuir monolayer is important?

ABSTRACT In this review we discuss about the immobilization of enzymes in Langmuir-Blodgett films in order to determine the catalytic properties of these biomacromolecules when adsorbed on solid supports. Usually, the conformation of enzymes depends on the environmental conditions imposed to them, including the chemical composition of the matrix, and the morphology and thickness of the film. In this review, we show an outline of manuscripts that report the immobilization of enzymes as LB films since the 1980’s, and also some examples of how the surface properties of the floating monolayer prepared previously to the transfer to the solid support are important to determine the efficiency of the resulting device

Membranes and bioactive lipids.

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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

Tethered Bilayer lipid membranes (tBLMs) : interest and applications for biological membrane investigations.

International audienceBiological membranes play a central role in the biology of the cell. They are not only the hydrophobic barrier allowing separation between two water soluble compartments but also a supra-molecular entity that has vital structural functions. Notably, they are involved in many exchange processes between the outside and inside cellular spaces. Accounting for the complexity of cell membranes, reliable models are needed to acquire current knowledge of the molecular processes occurring in membranes. To simplify the investigation of lipid/protein interactions, the use of biomimetic membranes is an approach that allows manipulation of the lipid composition of specific domains and/or the protein composition, and the evaluation of the reciprocal effects. Since the middle of the 80's, lipid bilayer membranes have been constantly developed as models of biological membranes with the ultimate goal to reincorporate membrane proteins for their functional investigation. In this review, after a brief description of the planar lipid bilayers as biomimetic membrane models, we will focus on the construction of the tethered Bilayer Lipid Membranes, the most promising model for efficient membrane protein reconstitution and investigation of molecular processes occurring in cell membranes

Biomietic membranes and biomolecule immobilisation strategies for nanobiotechnology applications

International audienceBiological membranes constitute a source of inspiration for making supramolecular assemblies which can be used in the design of biomimetic sensors. At the same time, the concept of using biomolecules as an elementary structure to develop self-assembled entities has received considerable attention. More particularly, the ability of amphiphilic molecules like lipids, to spontaneously organise into bilayers, is suitable to achieve biomimetic membrane models. The potential of two-dimensional molecular self-assemblies is clearly illustrated by Langmuir monolayers of lipids formed at an air/water interface, which can be used as models to acquire knowledge about the molecular recognition process occurring in biological membranes. Langmuir-Blodgett (LB) technology, based on the transfer of this interfacial monomolecular film onto a solid support, allows building up lamellar lipid stack, with an accurate control of thickness and molecular organisation. This technique offers the possibility to prepare ultrathin layers suitable for biomolecule immobilisation. We are presenting herein an overview of work performed in our group that sheds light on the formation of biomimetic LB membranes associating protein in a well-defined orientation. Two points will be addressed: investigations of protein/lipid interactions using lipid monolayers as membrane models and biosensing applications. The objectives are to highlight advantages of interfacial Langmuir monolayers and supported Langmuir-Blodgett films to investigate molecular interactions between biomolecules and lipid membrane components or to elaborate biomimetic membranes as sensing layers, respectively. The present paper also draws a general picture of non-conventional methods for biomolecule immobilisation and their applications for biochip developments. The technologies presented are based either on original solid supports or on innovative immobilisation processes. First, ''Macromolecules to PDMS transfer'' technique relying on the direct entrapment of macromolecules spots during PDMS polymerisation is proposed as an alternative for the easy and simple PDMS surface modification. Then, the electro-addressing of biomolecule-aryl diazonium adducts at the surface of conducting biochips will be presented and shown to be an interesting alternative to immobilisation processes based on surface functionalisation

Chelating Langmuir-Blodgett film: a new versatile chemiluminescent sensing layer for biosensor applications

International audienceThe present study reports the achievement of a new chemiluminescent sensing layer able to simultaneously (i) play an active role on ligand immobilization and (ii) serve as a catalyst in detection processes for label-free biosensor applications. This new type of active Langmuir−Blodgett (LB) monolayer has been designed by using a chelating lipid (Ni-NTA-DOGS). Thanks to the chelated metallic cation, this peculiar lipid exhibits luminol chemiluminescence catalysis properties in the presence of hydrogen peroxide. Upon biomolecule interaction through imidazole ring chelation (mediated by the metallic cation bound to the lipid headgroup), the chemiluminescent signal can be modulated. The first chemiluminescent signal acquisition experiments have shown a strong and homogeneous signal of the chelating layer. Upon histamine interactions, a histidine derivative used as a marker of fresh food quality, we succeeded in obtaining as a proof of concept a chemiluminescent signal variation without any derivatization of the target molecule. This signal variation was shown to be directly correlated to the histamine concentration with a limit of detection of 2 μg/mL