Laboratoire P.A.S.T.E.U.R

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Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones – what makes a good extraction pathway?

Photochem. Photobiol. Sci., 2016,15, 969-979


Plants or algae take many bene!ts from oxygenic photosynthesis by converting solar energy into chemical energy through the synthesis of carbohydrates from carbon dioxide and water. However, the overall yield of this process is rather low (about 4% of the total energy available from sunlight is converted into chemical energy). This is the principal reason why recently many studies have been devoted to extraction of photosynthetic electrons in order to produce a sustainable electric current. Practically, the electron transfer occurs between the photosynthetic organism and an electrode and can be assisted by an exogenous mediator, mainly a quinone. In this regard, we recently reported on a method involving "uorescence measurements to estimate the ability of di#erent quinones to extract photosynthetic electrons from a mutant of Chlamydomonas reinhardtii. In the present work, we used the same kind of methodology to establish a zone diagram for predicting the most suitable experimental conditions to extract photoelectrons from intact algae (quinone concentration and light intensity) as a function of the purpose of the study. This will provide further insights into the extraction mechanism of photosynthetic electrons using exogenous quinones. Indeed "uorescence measurements allowed us to model the capacity of photosynthetic algae to donate electrons to an exogenous quinone by considering a numerical parameter called “open center ratio” which is related to the Photosystem II acceptor redox state. Then, using it as a proxy for investigating the extraction of photosynthetic electrons by means of an exogenous quinone, 2,6-DCBQ, we suggested an extraction mechanism that was globally found consistent with the experimentally extracted parameters.

Temperature-Switchable Control of Ligand Display on Adlayers of Mixed Poly(lysine)‑g‑(PEO) and Poly(lysine)‑g‑(ligand-modified poly‑N‑isopropylacrylamide)

Biomacromolecules2016 May 9;17(5):1727-36


Adlayers of poly(lysine)-g -PEG comblike copolymer are extensively used to prepare cell-repellant and proteinrepellent surfaces by a straightforward coulomb-driven adsorption that is compatible with diverse substrates (glass, Petri dish, etc.). To endow surfaces with functional properties, namely, controlled ligand-protein binding, comblike poly(lysine) derivatives were used to deposit temperature-responsive poly(NIPAM) macrografts mixed with PEG ones on glass surfaces. Simple surface immersion in mixed solutions of biotin-modifi ed poly(lysine)-g -poly(N -isopropylacrylamide) and poly(lysine)-g -poly(ethylene oxide) yielded robust adlayers whose composition refl ected the ratio between the two polymers in solution. We show by fluorescence imaging, and comparison with repellent 100% PEGylated patterns, that specifi c binding of model avidin/particle conjugates (diameters of ca. 10 or 200 nm) was controlled by temperature switch. The biotin ligand was displayed and accessible at low T , or hidden at T  > LCST. Topography and mechanical mapping measurements by AFM confi rmed the swelling/collapse status of PNIPAM macrografts in the adlayer at low/high T , respectively. Temperature-responsive comblike PLL derivative that can spontaneously cover anionic interfaces is a promising platform enabling good control on the deposition and accessibility of biofunctional groups on various solid surfaces

Cellular heterogeneity mediates inherent sensitivity– specificity tradeoff in cancer targeting by synthetic circuits

Proc. Natl. Acad. Sci. USA2016


Synthetic gene circuits are emerging as a versatile means to target cancer with enhanced specificity by combinatorial integration of multiple expression markers. Such circuits must also be tuned to be highly sensitive because escape of even a few cells might be detrimental. However, the error rates of decision-making circuits in light of cellular variability in gene expression have so far remained unexplored. Here, we measure the single-cell response function of a tunable logicANDgate actingon twopromoters in heterogeneous cell populations. Our analysis reveals an inherent tradeoff between specificity and sensitivity that is controlled by the AND gate amplification gain and activation threshold. We implement a tumor-mimicking cellculture model of cancer cells emerging in a background of normal ones, and show that molecular parameters of the synthetic circuits control specificity and sensitivity in a killing assay. This suggests that, beyond the inherent tradeoff, synthetic circuits operating in a heterogeneous environment could be optimized to efficiently target malignant state with minimal loss of specificity.

On-Chip Quantitative Measurement of Mechanical Stresses During Cell Migration with Emulsion Droplets


Long-term in vivo single-cell lineage tracing of deep structures using three-photon activation

Light: Science & Applications (2016) 5, e16084


Genetic labeling techniques allow for noninvasive lineage tracing of cells in vivo. Two-photon inducible activators provide spatial resolution for superficial cells, but labeling cells located deep within tissues is precluded by scattering of the far-red illumination required for two-photon photolysis. Three-photon illumination has been shown to overcome the limitations of two-photon microscopy for in vivo imaging of deep structures, but whether it can be used for photoactivation remains to be tested. Here we show, both theoretically and experimentally, that three-photon illumination overcomes scattering problems by combining longer wavelength excitation with high uncaging three-photon cross-section molecules. We prospectively labeled heart muscle cells in zebrafish embryos and found permanent labeling in their progeny in adult animals with negligible tissue damage. This technique allows for a noninvasive genetic manipulation in vivo with spatial, temporal and cell-type specificity, and may have wide applicability in experimental biology.