Electrospray ionization mass spectrometry studies of noncovalent myosin VI complexes reveal a new specific calmodulin binding site

Among the myosin superfamily, myosin VI differs from all others by a reverse directionality and a particular motility. Little structural information is available for myosin VI. It is known that it binds one calmodulin (CaM) by means of a single "IQ motif" and that myosin VI contains a specific insert located at the junction between the motor domain (MD) and the lever arm, likely to play a critical role for the unusual motility previously observed. Electrospray ionization mass spectrometry (MS) was used to determine the CaM and Ca2+ stoichiometries in several myosin VI constructs. In particular, the experimental conditions required for the observation of multiprotein/Ca2+ noncovalent assemblies are detailed for two truncated MD constructs (less than 20 kDa) and for three full MD constructs (more than 90 KDa). The specificity of the detected stoichiometries is discussed for each construct and the resolving power of Time of Flight mass spectrometry is stressed, in particular for the detection of metal ions binding to high molecular weight complexes. MS reveals a new CaM binding site for myosin VI and highlights a different behavior for the five myosin VI constructs versus Ca2+ binding. In addition to these stoichiometry based experiments, gas-phase dissociation analyses on intact complexes are described. They reveal that Ca2+ transfer between protein partners occurs during the dissociation process for one construct with a full MD. Charge-transfer and dissociation behavior has allowed to draw structural assumptions for the interaction of the MD with the CaM N-terminal lobe.     

Dynamic behavior in diplatinum metalloreceptors

Diplatinum metalloreceptors anti-4a and anti-4b exhibit dynamic behavior in solution that is modified by anion binding. An X-ray crystal structure determination of anti-4a supports its proposed solution structure.     

Characterization of multimetallic grid-type complexes by electrospray mass spectrometry

The self-assembly of the terdentate ligands 1a-h, based on terpyridine-like binding sites, with octahedrally coordinated metal ions, such as Fe(II), Co(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II), leads to the formation of the supramolecular grid-type complexes 2a-c(M(II)), 3d-g(M(II)) and 4h(M(II)). The structures and compositions of these coordination complexes in solution were deduced from electrospray mass spectrometry (ESMS) measurements. The results agree with the data available from x-ray radiocrystallography in the solid state and/or NMR spectroscopy in solution. ESMS may be applied in cases where other methods are difficult to use or inconclusive. This study stresses the power of ESMS in supramolecular chemistry.     

A mixed-bridging ligand nonanuclear Ru(II) dendrimer containing a tris- chelating core. Synthesis and redox properties

The first ligand-cored dendrimer based on branching Ru(II) centers and containing mixed polypyridine bridging ligands has been prepared; redox experiments suggest that the redox-active core is not reduced at the expected potential, probably as a consequence of shielding induced by the rigid dendritic array.     

Mass spectrometric studies of phosphodiesters linked to oxysterols and nucleosides,a family of biologically potent oxygenated sterols

Negative-ion fast atom bombardment mass spectra of five compounds resulting from combinations between oxysterols and nucleoside analogues linked by phosphodiester bonds are presented and interpreted. This method seems to be the most appropriate for elucidating the structure of these complex, labile and non-volatile phosphate-containing molecules which exhibit important antitumour and/or immunosuppressive activities.     

Alkali cation induced liquid crystalline properties of an oligophenylenevinylene-benzocrown ether conjugate

An oligophenylenevinylene-benzocrown ether conjugate has been prepared and its binding selectivity for alkali metal ions evaluated by electrospray mass spectrometry. Whereas this benzocrown-ether derivative does not exhibit any liquid crystalline properties, the self-assembly by coordination to potassium or cesium leads to supramolecular sandwich complexes with mesomorphic properties.     

Quantum-state diffusion with adaptive noise

We present a scheme for stochastic quantum-state diffusion (QSD) with adaptive noise to calculate the time evolution of an arbitrary observable of an open system. The method is based on the fact that the observable is much less sensitive to adaptive noise than to noise with a random phase. Hence, the individual realisations of the expectation value of the observable stay closer to the average evolution and fewer realisations are required to obtain the ensemble average. This is illustrated by applying QSD to a driven two-level system using both randomly phased and adaptive noise. Applying QSD with adaptive noise to an undriven two-level system enables us to derive a deterministic Schr?dinger equation that produces the exact evolution of an arbitrary observable. Received: 31 July 1997 / Received in final form: 12 February 1998 / Accepted: 13 March 1998     

Nuclear proteome analysis of undifferentiated mouse embryonic stem and germ cells

Embryonic stem cells (ESCs) and embryonic germ cells (EGCs) provide exciting models for understanding the underlying mechanisms that make a cell pluripotent. Indeed, such understanding would enable dedifferentiation and reprogrammation of any cell type from a patient needing a cell therapy treatment. Proteome analysis has emerged as an important technology for deciphering these biological processes and thereby ESC and EGC proteomes are increasingly studied. Nevertheless, their nuclear proteomes have only been poorly investigated up to now. In order to investigate signaling pathways potentially involved in pluripotency, proteomic analyses have been performed on mouse ESC and EGC nuclear proteins. Nuclei from ESCs and EGCs at undifferentiated stage were purified by subcellular fractionation. After 2‐D separation, a subtractive strategy (subtracting culture environment contaminating spots) was applied and a comparison of ESC, (8.5 day post coïtum (dpc))‐EGC and (11.5 dpc)‐EGC specific nuclear proteomes was performed. A total of 33 ESC, 53 (8.5 dpc)‐EGC, and 36 (11.5 dpc)‐EGC spots were identified by MALDI‐TOF‐MS and/or nano‐LC‐MS/MS. This approach led to the identification of two isoforms (with and without N‐terminal acetylation) of a known pluripotency marker, namely developmental pluripotency associated 5 (DPPA5), which has never been identified before in 2‐D gel‐MS studies of ESCs and EGCs. Furthermore, we demonstrated the efficiency of our subtracting strategy, in association with a nuclear subfractionation by the identification of a new protein (protein arginine N‐methyltransferase 7; PRMT7) behaving as proteins involved in pluripotency.     

Inertial manifolds of parabolic differential equations under high-order discretizations

This paper deals with the long-time behaviour of numerical discretizationsof nonlinear parabolic differential equations. For various equationsof mathematical physics, the dynamics are governed by a finite-dimensionalinertial manifold, which attracts solutions at an exponentialrate. We show that Runge-Kutta time and spectral Galerkin spacediscretizations possess inertial manifolds which approximatethe inertial manifold of the continuous problem with the orderof finite-time approximations of smooth solutions. We thus obtainestimates for the distance between the inertial manifolds ofthe partial differential equation and its semi- and full discretizationswhich show the high order of the time discretization and exponentiallyfast convergence of the space discretization. These resultsare obtained by using time analyticity and Gevrey regularityof solutions of the differential equation. As an applicationof the theory, the complex Ginzburg-Landau equation is considered.