Jean-Marc Valleton

Hypothesis: Hyperstructures regulate bacterial structure and the cell cycle

A myriad different constituents or elements (genes, proteins, lipids, ions, small molecules etc.) participate in numerous physico-chemical processes to create bacteria that can adapt to their environments to survive, grow and, via the cell cycle, reproduce. We explore the possibility that it is too difficult to explain cell cycle progression in terms of these elements and that an intermediate level of explanation is needed. This level is that of hyperstructures. A hyperstructure is large, has usually one particular function, and contains many elements. Non-equilibrium, or even dissipative, hyperstructures that, for example, assemble to transport and metabolize nutrients may comprise membrane domains of transporters plus cytoplasmic metabolons plus the genes that encode the hyperstructures enzymes. The processes involved in the putative formation of hyperstructures include: metabolite-induced changes to protein affinities that result in metabolon formation, lipid-organizing forces that result in lateral and transverse asymmetries, post-translational modifications, equilibration of water structures that may alter distributions of other molecules, transertion, ion currents, emission of electromagnetic radiation and long range mechanical vibrations. Equilibrium hyperstructures may also exist such as topological arrays of DNA in the form of cholesteric liquid crystals. We present here the beginning of a picture of the bacterial cell in which hyperstructures form to maximize efficiency and in which the properties of hyperstructures drive the cell cycle.

Surface modification by low-pressure glow discharge plasma of an unsaturated polyester resin: effect on water diffusivity and permeability

Abstract Unsaturated polyester resin (UPR) films have been modified by a tetrafluoromethane microwave plasma. The treated surface morphologies investigated by contact angle, atomic force microscopy and permeation measurements show that the CF 4 plasma treatment decreases drastically the surface energy by increasing the hydrophobic character. The surface modification due to plasma fluorination decreases the water content diffusing through the UPR film and the time lag diffusion coefficient and thus, the sorption kinetic. From these results, it is clearly shown that the CF 4 plasma treated layer improves drastically the barrier effects.

Elaboration of a glucose biosensor based on Langmuir-Blodgett technology

Abstract The elaboration of a biosensor based on Langmuir-Blodgett technology has been studied. The device is based on the use of a mixed monolayer of behenic acid and glucose oxidase. The biosensor is characterized by short response times (a few seconds), and by a quasi-linearity of the response signal as a function of glucose concentration.

Molecular resolution images of enzyme-containing Langmuir-Blodgett films

Abstract Langmuir-Blodgett technology has been used for fabricating systems consisting of mixed layers of behenic acid and glucose oxidase. These systems have been imaged by atomic force microscopy at a molecular level. The observation of these samples shows the presence of the glucose oxidase molecules organized in parallel ridges, and individual behenic acid molecules are clearly visible on top of the enzyme molecules. The dimensions of the structures observed are consistent with available data.

Interaction of FtsZ protein with a DPPE Langmuir film

Abstract FtsZ is the key protein in cell division in bacteria. We have proposed that lipid domains in the cytoplasmic membrane play a role in the localisation of FtsZ. In order to test this hypothesis, we used a model system based on Langmuir films to simulate the bacterial membrane. In this simple system we used a single phospholipid, dipalmytoylphosphatidylethanolamine, which is the major constituent of the inner membrane in Escherichia coli. The first results show clearly the importance of the GTP-controlled assembly process in the appearance of circular or fibrillar structures.

Inner membrane lipids of Escherichia coli form domains.

In prokaryotic cells, the hypothesis of the existence of lipid domains was considered. In order to test this hypothesis and study the organization of lipids in the inner membrane of Escherichia coli, we elaborated Langmuir films mimicking the inner leaflet of this membrane by considering lipids extracted from the inner membrane of E coli by Folch protocol. Lipid monolayers were elaborated by using these extracts (Langmuir technique); the organization of the resulting films was studied at the air-water interface by Brewster angle microscopy and after transfer onto muscovite by atomic force microscopy. The existence of domains was demonstrated for different interfacial pressures of biological interest, and their stability was studied.

Characterization of behenic acid/glucose oxidase Langmuir—Blodgett films by spectrophotometry: a tentative model of their organization

Abstract Mixed behenic acid/glucose oxidase ( BA GOx ) films were transferred onto CaF2 slides and gold substrates and characterized by IR and/or UV-visible spectroscopies. The results obtained were confirmed by the study of pressure-area isotherms and led to a diagrammatic model of the structure elaborated by Langmuir—Blodgett technology. This structure could present some domains with GOx organized as islets.

Scanning force microscopy investigation of amphiphilic cyclodextrin Langmuir-Blodgett films

Abstract The structures of α, β and γ per-azido cyclodextrin Langmuir-Blodgett films were compared using scanning force microscopy. At the micrometre scale, the crystalline nature of the β derivative films is clearly observed, whereas a and γ derivative films are more continuous. At the molecular scale, the hexagonal arrangement of the β derivative films is easily imaged, whereas a derivative films are imaged with difficulty, and the images obtained with γ derivative films have poor quality. At an intermediate scale, hexagonal superstructures can be observed with the β derivative.

Analysis of the dynamic organization of mixed protein/fatty acid Langmuir films

Abstract The dynamic organization of a mixed Langmuir film of glucose oxidase and behenic acid has been studied. Samples of the mixed film transferred after different relaxation times were analyzed by UV-Vis and IR spectroscopies and by lateral force microscopy. The results demonstrate that the enzyme molecules present at the air/water interface arc progressively covered by the behenic acid film. Moreover, we observe an increase of the quantity of glucose oxidase in the mixed film with lime, showing that the adsorption of glucose oxidase under the behenic acid film continues during and after the relaxation process.

Information processing in biomolecule-based biomimetic systems. From macroscopic to nanoscopic scale

Abstract This paper deals with information processing in biomolecule-based biomimetic systems (i.e., artificial systems in which a biomolecule is involved, and whose purpose is to mimic biological functions). Several approaches are presented, based on structures ranging from the macroscopic to the nanoscopic scale. The first part is devoted to the biosensing function: the basic principle, the possible transducers, the main applications. The second part presents integrated information on processing functions in macroscopic structures: active transport, biological clocks, mathematical operations, information storage and control functions. In the third part, the evolution of this field toward the nanoscopic scale is described, with the presentation of some methods of creating nanoscopic structures (adsorbed and chemically bound monolayers, black lipid membrane (BLM) and Langmuir-Blodgett techniques), and their application in the field of biosensors. Finally, new trends in information processing by nanoscopic systems are discussed.