Jean-Philippe Demers

Max Planck Institute for Biophysical Chemistry, Göttingen, Lower Saxony, Germany

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Publications (14)84.87 Total impact

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    Pascal Fricke, Jean-Philippe Demers, Stefan Becker, Adam Lange
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    ABSTRACT: Bacterial T3SS needles formed by the protein MxiH are studied using DNP-enhanced ssNMR spectroscopy at 14.1 T (600 MHz). This technique provides spectra of good resolution, allowing us to draw conclusions about the protein dynamics. With the obtained signal enhancement, samples of limited quantity now get within reach of ssNMR studies.
    ChemPhysChem 11/2013; · 3.35 Impact Factor
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    ABSTRACT: The Type Three Secretion System (T3SS), or injectisome, is a macromolecular infection machinery present in many pathogenic Gram-negative bacteria. It consists of a basal body, anchored in both bacterial membranes, and a hollow needle through which effector proteins are delivered into the target host cell. Two different architectures of the T3SS needle have been previously proposed. First, an atomic model of the Salmonella typhimurium needle was generated from solid-state NMR data. The needle subunit protein, PrgI, comprises a rigid-extended N-terminal segment and a helix-loop-helix motif with the N-terminus located on the outside face of the needle. Second, a model of the Shigella flexneri needle was generated from a high-resolution 7.7-Å cryo-electron microscopy density map. The subunit protein, MxiH, contains an N-terminal α-helix, a loop, another α-helix, a 14-residue-long β-hairpin (Q51-Q64) and a C-terminal α-helix, with the N-terminus facing inward to the lumen of the needle. In the current study, we carried out solid-state NMR measurements of wild-type Shigella flexneri needles polymerized in vitro and identified the following secondary structure elements for MxiH: a rigid-extended N-terminal segment (S2-T11), an α-helix (L12-A38), a loop (E39-P44) and a C-terminal α-helix (Q45-R83). Using immunogold labeling in vitro and in vivo on functional needles, we located the N-terminus of MxiH subunits on the exterior of the assembly, consistent with evolutionary sequence conservation patterns and mutagenesis data. We generated a homology model of Shigella flexneri needles compatible with both experimental data: the MxiH solid-state NMR chemical shifts and the state-of-the-art cryoEM density map. These results corroborate the solid-state NMR structure previously solved for Salmonella typhimurium PrgI needles and establish that Shigella flexneri and Salmonella typhimurium subunit proteins adopt a conserved structure and orientation in their assembled state. Our study reveals a common structural architecture of T3SS needles, essential to understand T3SS-mediated infection and develop treatments.
    PLoS Pathogens 03/2013; 9(3):e1003245. · 8.14 Impact Factor
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    ABSTRACT: The unambiguous stereospecific assignment of the prochiral methyl groups in Val and Leu plays an important role in the structural investigation of proteins by NMR. Here, we present a straightforward method for their stereospecific solid-state NMR assignment based on [2-(13)C]Glucose ([2-(13)C]Glc) as the sole carbon source during protein expression. The approach is fundamentally based on the stereo-selective biosynthetic pathway of Val and Leu, and the co-presence of [2-(13)C]pyruvate produced mainly by glycolysis and [3-(13)C]/[1,3-(13)C]pyruvate most probably formed through scrambling in the pentose phosphate pathway. As a consequence, the isotope spin pairs (13)Cβ-(13)Cγ2 and (13)Cα-(13)Cγ1 in Val, and (13)Cγ-(13)Cδ2 and (13)Cβ-(13)Cδ1 in Leu are obtained. The approach is successfully demonstrated with the stereospecific assignment of the methyl groups of Val and Leu of type 3 secretion system PrgI needles and microcrystalline ubiquitin.
    Journal of Magnetic Resonance 01/2013; 228C:45-49. · 2.30 Impact Factor
  • Medecine sciences: M/S 11/2012; 28(11):926-928. · 0.56 Impact Factor
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    ABSTRACT: The voltage-dependent anion channel (VDAC) is the major protein in the outer mitochondrial membrane, where it mediates transport of ATP and ADP. Changes in its permeability, induced by voltage or apoptosis-related proteins, have been implicated in apoptotic pathways. The three-dimensional structure of VDAC has recently been determined as a 19-stranded β-barrel with an in-lying N-terminal helix. However, its gating mechanism is still unclear. Using solid-state NMR spectroscopy, molecular dynamics simulations, and electrophysiology, we show that deletion of the rigid N-terminal helix sharply increases overall motion in VDAC's β-barrel, resulting in elliptic, semicollapsed barrel shapes. These states quantitatively reproduce conductance and selectivity of the closed VDAC conformation. Mutation of the N-terminal helix leads to a phenotype intermediate to the open and closed states. These data suggest that the N-terminal helix controls entry into elliptic β-barrel states which underlie VDAC closure. Our results also indicate that β-barrel channels are intrinsically flexible.
    Structure 07/2012; 20(9):1540-9. · 5.99 Impact Factor
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    ABSTRACT: An abnormal N-heterocyclic carbene (aNHC) has been used as a Lewis base to initiate dismutation of trichlorosilane. This report presents the reactivity differences of a normal N-heterocyclic carbene (NHC) versus aNHC with heavier group 14 elements. Three novel compounds (NHC)(2)·SiCl(2)H(2) (2), aNHC·SiCl(2)H(2) (3), and aNHC·GeCl(2) (4) have been synthesized and characterized by single crystal X-ray analysis, solid-state NMR and DFT calculations.
    Chemical Communications 06/2012; 48(61):7574-6. · 6.38 Impact Factor
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    ABSTRACT: Herein we report the syntheses of terminal Sn(II) (3) and Ge(II) (4) hydrides from the corresponding chloride precursors [{2,6-iPr(2)C(6)H(3)NCMe}(2)C(6)H(3)MCl] (M = Sn (1), Ge (2)) using [K{B(sec-Bu)(3)}H] as a hydrogenating agent. Combination of steric shielding and intramolecular N → M interactions resulted in the protection of M(II)-H bonds.
    Chemical Communications 04/2012; 48(40):4890-2. · 6.38 Impact Factor
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    ABSTRACT: Cationic and anionic species of heavier low-valent group 14 elements are intriguing targets in main group chemistry due to their synthetic potential and industrial applications. In the present study, we describe the synthesis of cationic (MCl(+)) and anionic (MCl(3)(-)) species of heavier low-valent group 14 elements of germanium(II) and tin(II) by using the substituted Schiff base 2,6-diacetylpyridinebis(2,6-diisopropylanil) as Lewis base (LB). Treatment of LB with 2 equiv of GeCl(2)·dioxane and SnCl(2) in toluene gives compounds [(LB)Ge(II)Cl](+)[Ge(II)Cl(3)](-) (1) and [(LB)Sn(II)Cl](+)[Sn(II)Cl(3)](-) (2), respectively, which possess each a low-valent cation and an anion. Compounds 1 and 2 are well characterized with various spectroscopic methods and single crystal X-ray structural analysis.
    Journal of the American Chemical Society 03/2012; 134(10):4998-5003. · 10.68 Impact Factor
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    ABSTRACT: This article reports the reduction of [{2,6-iPr(2)C(6)H(3)NC(CH(3))}(2)C(6)H(3)SnCl] (1) with potassium graphite to afford a new distannyne [{2,6-iPr(2)C(6)H(3)NC(CH(3))}(2)C(6)H(3)Sn](2) (2) with a Sn-Sn bond. The most striking phenomenon of 2 is the presence of two differently coordinated Sn atoms (one is three-coordinated, the other is four-coordinated). The Sn-Sn bond length in 2 is 2.8981(9) Å, which is very close to that of a Sn-Sn single bond (2.97-3.06 Å). To elucidate the nature of the Sn-Sn bond, DFT calculation is carried out that shows there is no multiple bond character in 2. Furthermore, the reaction of 2 with white P(4) affords the tetraphosphabicylobutane derivative 3. This is the first example of gentle activation of white phosphorus by a compound with low valent Sn atoms. Note that, unlike 2, in 3 both Sn atoms are four-coordinated.
    Journal of the American Chemical Society 09/2011; 133(44):17889-94. · 10.68 Impact Factor
  • Jean-Philippe Demers, Veniamin Chevelkov, Adam Lange
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    ABSTRACT: Recent progress in multi-dimensional solid-state NMR correlation spectroscopy at high static magnetic fields and ultra-fast magic-angle spinning is discussed. A focus of the review is on applications to protein resonance assignment and structure determination as well as on the characterization of protein dynamics in the solid state. First, the consequences of ultra-fast spinning on sensitivity and sample heating are considered. Recoupling and decoupling techniques at ultra-fast MAS are then presented, as well as more complex experiments assembled from these basic building blocks. Furthermore, we discuss new avenues in biomolecular solid-state NMR spectroscopy that become feasible in the ultra-fast spinning regime, such as sensitivity enhancement based on paramagnetic doping, and the prospect of direct proton detection.
    Solid State Nuclear Magnetic Resonance 08/2011; 40(3):101-13. · 2.10 Impact Factor
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    ABSTRACT: It's hip to be square: The reaction of amidinato chlorosilylene (PhC(NtBu)2SiCl) with adamantyl phosphaalkyne and white phosphorus affords the formation of Si-C-Si-P and Si-P-Si-P (see picture) four-membered rings. Both compounds were characterized by single-crystal X-ray studies and by solution and solid-state NMR spectroscopy. DFT calculations elucidated the bonding situation.
    Angewandte Chemie International Edition 03/2011; 50(10):2322–2325. · 11.34 Impact Factor
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    ABSTRACT: In contrast to the rich and ubiquitous chemistry displayed by silicon, [1] the chemistry of unsaturated four-membered het-erocycles containing silicon and phosphorus is not known. This situation is perhaps due to the instability associated with antiaromaticity for the cyclobutadiene ring systems, although it is known that the introduction of heteroatoms will substantially stabilize such rings. In a 1998 review, Bertrand clarified the bonding situation of four-membered hetero-cycles with four p electrons containing a phosphorus atom that has no p orbital available for contributing to the p system. [2] He showed that in these compounds either there is interrupted cyclic p delocalization or they are stable owing to a zwitterionic character, and he concluded that these compounds are not antiaromatic. This observation prompted us to design four-membered rings containing silicon and phosphorus as heteroatoms and to elucidate their bonding properties. Furthermore, nitrogen-or phosphorus-doped SiC systems have commercial applications as semiconducting materials. [3] The easy availability of heteroleptic chlorosilylene LSiCl (1) [4b] and bis-silylene (LSiÀSiL) (2) [5] (L = PhC(NtBu) 2) creates new dimensions in silicon chemistry. The reactions of these systems with unsaturated organic compounds are thermodynamically favorable owing to the oxidation of silicon from the divalent to the tetravalent state. [4b, 6] Herein we report the synthesis of the 1,3-disilacarbaphosphide 3, containing three heteroatoms, that resulted from the reac-tions of 1 and 2 with RCP under cleavage of the CP bond. The synthesis of 3 is straightforward. Addition of a toluene solution of 1-Ad À C P to the toluene solution of 1 at À30 8C in 1:3 molar ratio resulted in the formation of 3, which was isolated in 68.2 % yield as reddish-yellow air-and moisture-sensitive crystals (Scheme 1). The constitution of 3 was unequivocally characterized by single-crystal X-ray diffraction. [7] Figure 1 depicts the molecular view of 3, while selected bond lengths and bond angles are provided in the legend of Figure 1. Compound 3 crystallizes in the ortho-rhombic space group P2 1 2 1 2 1 . The core structure consists of two silicon atoms, one carbon atom, and one phosphorus atom, which together form a SiK -C-Si-P L four-membered ring. The predominant structural feature of 3 is the "naked" phosphorus atom, which connects the two silicon atoms. The two silicon atoms are each four-coordinate and display a distorted tetrahedral geometry by coordination with two nitrogen atoms from the amidinato ligand. The remaining two Scheme 1. Preparation of compound 3.
    · 11.34 Impact Factor
  • Jean-Philippe Demers, Vinesh Vijayan, Stefan Becker, Adam Lange
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    ABSTRACT: High static magnetic fields and very fast magic-angle spinning (MAS) promise to improve resolution and sensitivity of solid-state NMR experiments. The fast MAS regime has permitted the development of low-power cross-polarization schemes, such as second-order cross-polarization (SOCP), which prevent heat deposition in the sample. Those schemes are however limited in bandwidth, as weak radio-frequency (RF) fields only cover a small chemical shift range for rare nuclei (e.g. (13)C). Another consideration is that the efficiency of cross-polarization is very sensitive to magnetization decay that occurs during the spin-lock pulse on the abundant nuclei (e.g. (1)H). Having characterized this decay in glutamine at 60 kHz MAS, we propose two complementary strategies to tailor cross-polarization to desired spectral regions at low RF power. In the case of multiple sites with small chemical shift dispersion, a larger bandwidth for SOCP is obtained by slightly increasing the RF power while avoiding recoupling conditions that lead to fast spin-lock decay. In the case of two spectral regions with large chemical shift offset, an extension of the existing low-power schemes, called MOD-CP, is introduced. It consists of a spin-lock on (1)H and an amplitude-modulated spin-lock on the rare nucleus. The range of excited chemical shifts is assessed by experimental excitation profiles and numerical simulation of an I(2)S spin system. All SOCP-based schemes exhibit higher sensitivity than high-power CP schemes, as demonstrated on solid (glutamine) and semi-solid (hydrated, micro-crystalline ubiquitin) samples.
    Journal of Magnetic Resonance 08/2010; 205(2):216-23. · 2.30 Impact Factor
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    ChemPhysChem 08/2009; 10(13):2205-8. · 3.35 Impact Factor