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

Printer-friendly version

Chiral Crystal Packing Induces Enhancement of Vibrational Circular Dichroism

Angew. Chem. Int. Ed. 2018, 57, 13344 –13348

 

We demonstrate that molecular vibrations with originally low or zero intensity in a vibrational circular dichroism (VCD) spectrum attain chirality in molecular crystals by coordinated motion of the atoms. Ab initio molecular dynamics simulations of anharmonic solid-state VCD spectra of l-alanine crystals reveal how coherent vibrational modes exploit the space groupQs chirality, leading to nonlocal, enhanced VCD features, most significantly in the carbonyl region of the spectrum. The VCD-enhanced signal is ascribed to a helical arrangement of the oscillators in the crystal layers. No structural irregularities need to be considered to explain the amplification, but a crucial point lies in the polarization of charge, which requires an accurate description of the electronic structure. Delivering a quantitative atomic conception of supramolecular chirality induction, our ab initio scheme is applicable well beyond molecular crystals, for example, to address VCD in proteins and related compounds.

Investigation of photocurrents resulting froma living unicellular algae suspension with quinones over time

Chem. Sci.2018

Plants, algae, and some bacteria convert solar energy into chemical energy by using photosynthesis. In light of the current energy environment, many research strategies try to benefit from photosynthesis in order to generate usable photobioelectricity. Among all the strategies developed for transferring electrons from the photosynthetic chain to an outer collecting electrode, we recently implemented a method on a preparative scale (high surface electrode) based on a Chlamydomonas reinhardtii green algae suspension in the presence of exogenous quinones as redox mediators. While giving rise to an interesting performance (10–60 μA cm−2) in the course of one hour, this device appears to cause a slow decrease of the recorded photocurrent. In this paper, we wish to analyze and understand this gradual fall in performance in order to limit this issue in future applications. We thus first show that this kind of degradation could be related to over-irradiation conditions or side-effects of quinones depending on experimental conditions. We therefore built an empirical model involving a kinetic quenching induced by incubation with quinones, which is globally consistent with the experimental data provided by fluorescence measurements achieved after dark incubation of algae in the presence of quinones.

 

 

Improved chemical-genetic fluorescent markers for live cell microscopy

Biochemistry2018, 57 (39), pp 5648–5653

 

Inducible chemical-genetic fluorescent markers are promising tools for live cell imaging requiring high spatiotemporal resolution and low background fluorescence. The Fluorescence-Activating and absorption Shifting Tag (FAST) was recently developed to form fluorescent molecular complexes with a family of small, synthetic fluorogenic chromophores (so-called fluorogens). Here, we use rational design to modify the binding pocket of the protein and screen for improved fluorescence performances with four different fluorogens. The introduction of a single mutation results in improvements in both quantum yield and dissociation constant with nearly all fluorogens tested. Our improved FAST (iFAST) allowed the generation of a tandem td-iFAST that forms green and red fluorescent reporters 1.6-fold and 2-fold brighter than EGFP and mCherry, respectively, while having comparable size.

 

 

Actin-Network Architecture Regulates Microtubule Dynamics

Curr Biol. (16) 2018 : 2647-2656

 

In Brief Colin et al. show that branched actin networks block microtubule growth and trigger microtubule disassembly using Xenopus egg extracts and in vitro reconstituted systems. This demonstrates the role of actin-network architecture in regulating microtubule dynamics. 

 

Highlights 

·     Branched actin networks block microtubule growth and trigger their disassembly 

·     Unbranched actin networks do not interfere with microtubule growth 

·     Branched actin networks perturb meiotic spindle assembly in Xenopusegg extracts

 

Circularly permuted fluorogenic proteins for the design of modular biosensors

ACS Chem. Biol. 2018

Fluorescent reporters are essential components for the design of optical biosensors able to image intracellular analytes in living cells. Herein, we describe the development of circularly permuted variants of Fluorescence-Activating and absorption-Shifting Tag (FAST) and demonstrate their potential as reporting module in biosensors. Circularly permutated FAST (cpFAST) variants allow one to condition the binding and activation of a fluorogenic ligand (and thus fluorescence) to analyte recognition by coupling them with analyte-binding domains. We demonstrated their use for biosensor design by generating multicolor plug-and-play fluorogenic biosensors for imaging the intracellular levels of Ca2+in living mammalian cells in real-time.