Conformational selection underlies recognition of a molybdoenzyme by its dedicated chaperone

Molecular recognition is central to all biological processes. Understanding the key role played by dedicated chaperones in metalloprotein folding and assembly requires the knowledge of their conformational ensembles. In this study, the NarJ chaperone dedicated to the assembly of the membrane-bound respiratory nitrate reductase complex NarGHI, a molybdenum-iron containing metalloprotein, was taken as a model of dedicated chaperone. The combination of two techniques ie site-directed spin labeling followed by EPR spectroscopy and ion mobility mass spectrometry, was used to get information about the structure and conformational dynamics of the NarJ chaperone upon binding the N-terminus of the NarG metalloprotein partner. By the study of singly spin-labeled proteins, the E119 residue present in a conserved elongated hydrophobic groove of NarJ was shown to be part of the interaction site. Moreover, doubly spin-labeled proteins studied by pulsed double electron-electron resonance (DEER) spectroscopy revealed a large and composite distribution of inter-label distances that evolves into a single preexisting one upon complex formation. Additionally, ion mobility mass spectrometry experiments fully support these findings by revealing the existence of several conformers in equilibrium through the distinction of different drift time curves and the selection of one of them upon complex formation. Taken together our work provides a detailed view of the structural flexibility of a dedicated chaperone and suggests that the exquisite recognition and binding of the N-terminus of the metalloprotein is governed by a conformational selection mechanism

Angular Dependences of Third Harmonic Generation from Microdroplets

We present experimental and theoretical results for the angular dependence of third harmonic generation (THG) of water droplets in the micrometer range (size parameter $62<ka<248$). The THG signal in $p$- and $s$-polarization obtained with ultrashort laser pulses is compared with a recently developed nonlinear extension of classical Mie theory including multipoles of order $l\leq250$. Both theory and experiment yield over a wide range of size parameters remarkably stable intensity maxima close to the forward and backward direction at ``magic angles''. In contrast to linear Mie scattering, both are of comparable intensity.Comment: 4 pages, RevTeX, 3 figures available on request from [email protected], submitted to PR

Mesoporous Silica Nanoparticles Loaded with Surfactant: Low Temperature Magic Angle Spinning 13C and 29Si NMR Enhanced by Dynamic Nuclear Polarization

We show that dynamic nuclear polarization (DNP) can be used to enhance NMR signals of13C and 29Si nuclei located in mesoporous organic/inorganic hybrid materials, at several hundreds of nanometers from stable radicals (TOTAPOL) trapped in the surrounding frozen disordered water. The approach is demonstrated using mesoporous silica nanoparticles (MSN), functionalized with 3-(N-phenylureido)propyl (PUP) groups, filled with the surfactant cetyltrimethylammonium bromide (CTAB). The DNP-enhanced proton magnetization is transported into the mesopores via 1H–1H spin diffusion and transferred to rare spins by cross-polarization, yielding signal enhancements εon/off of around 8. When the CTAB molecules are extracted, so that the radicals can enter the mesopores, the enhancements increase to εon/off ≈ 30 for both nuclei. A quantitative analysis of the signal enhancements in MSN with and without surfactant is based on a one-dimensional proton spin diffusion model. The effect of solvent deuteration is also investigated

Stabilization of copper nanoparticles in zeolite suspensions

International audienc

Copper containing zeolites thin films for light driven host guest chemistry

International audienc

Copper containing zeolites thin films for light driven host guest chemistry

International audienc

Stabilization of copper nanoparticles in zeolite suspensions

International audienc

Formation of copper nanoparticles in LTL nanosized zeolite: spectroscopic characterization

International audienceThe state of copper species stabilized in nanosized LTL zeolite subjected to various post-synthesis treatments was unveiled by a range of spectroscopic techniques. FTIR and UV-Vis studies demonstrated that the reduction process of copper in the LTL nanosized zeolite leads to the formation of different species including Cu2+, Cu+ and Cu nanoparticles (Cu NPs). The adsorption of probe molecules (NO and CO) was used to selectively monitor the copper species in the LTL nanosized zeolite upon oxidation and reduction post-synthesis treatments. Both the Cu2+ and Cu+ species were probed by NO and CO, respectively. The amount of Cu+ in the LTL zeolite nanocrystals was about 43% as determined by FTIR, while the amount of Cu NPs was about 55% determined by the UV-Vis spectroscopic characterization. These results were complemented by EPR, 29Si and 63Cu MAS NMR spectroscopic data. The EPR spectroscopy was further applied to monitor the effective reduction of the Cu2+ species and their re-oxidation, while the 63Cu MAS NMR verified the presence of Cu NPs in the LTL nanosized zeolite crystals

Study of gallium arsenide on silicon by small angle X-ray scattering

In order to study the heteroepitaxial growth of gallium arsenide on silicon (100), Small Angle X-ray Scattering (SAXS) experiments have been performed at the synchrotron radiation facility Photon Factory at KEK. The samples studied have been grown by both Atomic Layer Epitaxy and Metal-Organic Chemical Vapor Deposition. The two dimensional SAXS patterns present different features depending on the growth technique.Afin d'étudier la croissance hétéroépitaxiale de l'arséniure de gallium sur silicium (00l), des expériences de diffusion centrale des rayons X ont été effectuées au rayonnement synchrotron Photon Factory au KEK. Les echantillons etudies ont été élaborés par Atomic Layer Epitaxy et par Metal-Organic Chemical Vapor Deposition. Les courbes bidimensionnelles de diffusion centrale présentent différentes caractéristiques selon la technique de déposition