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Host cell invasion by the facultative intracellular pathogen Listeria monocytogenes requires the invasion protein InlB in many cell types. InlB consists of an N-terminal internalin domain that binds the host cell receptor tyrosine kinase Met and C-terminal GW domains that bind to glycosaminoglycans (GAGs). Met binding and activation is required for host cell invasion, while the interaction between GW domains and GAGs enhances this effect. Soluble InlB elicits the same cellular phenotypes as the natural Met ligand hepatocyte growth factor/scatter factor (HGF/SF), e.g. cell scatter. So far, little is known about the central part of InlB, the B-repeat. Here we present a structural and functional characterization of the InlB B-repeat. The crystal structure reveals a variation of the β-grasp fold that is most similar to small ubiquitin-like modifiers (SUMOs). However, structural similarity also suggests a potential evolutionary relation to bacterial mucin-binding proteins. The B-repeat defines the prototype structure of a hitherto uncharacterized domain present in over a thousand bacterial proteins. Generally, this domain probably acts as a spacer or a receptor-binding domain in extracellular multi-domain proteins. In cellular assays the B-repeat acts synergistically with the internalin domain conferring to it the ability to stimulate cell motility. Thus, the B-repeat probably binds a further host cell receptor and thereby enhances signaling downstream of Met.
Pyrazolyl-substituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives have been synthesized by reaction of 1,4-benzoquinone and 1,4-naphthoquinone, respectively, with pyrazole. Cyclovoltammetric measurements have shown that 1,4-benzoquinone possesses the potential to oxidize 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene. The 2,5-bis(pyrazol-1-yl)- 1,4-dihydroxybenzene reacts with air to give quantitatively black insoluble 2,5-bis(pyrazol-1-yl)-1,4- quinhydrone. Black crystals of 2,5-bis(pyrazol-1-yl)-1,4-quinhydrone suitable for X-ray diffraction were grown from methanol at ambient temperature (monoclinic C2/c). The poor yields of pyrazolylsubstituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives can be explained by the formation of insoluble black quinhydrons in the reaction of benzoquinone and naphthoquinone with pyrazole. The dianions of 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene react with oxygen to give the corresponding semiquinone anions. 2,5-Bis(pyrazol-1-yl)-1,4-benzoquinone shows two reversible one-electron reduction processes in cyclovoltammetric measurements, whereas pyrazolyl-substituted 1,4-dihdroxybenzene and -naphthene derivatives undergo irreversibile electrontransfer processes.
The two-electron reduction of tetraphenyl-p-quinodimethane M via its radical anion M⊖ to its dianion M⊖⊖ is explored both by cyclovoltammetry and ESR/ENDOR spectroscopy. Contact of the diglyme solution with added 15-crown-5 under aprotic conditions with a sodium metal mirror yields black crystals of a solvent-separated contact ion triple [M⊖⊖][Na⊕(OCH2CH2)5(H3CO(CH2CH2O)2CH3)]2. The two-electron-insertion into the pquinodimethane derivative R2C⊖=C(HC=CH)2C=CR2 changes its structure drastically to that of a twofold carbanion substituted benzene, R2C⊖ -(C6H4)- ⊖CR2. MNDO calculations provide a rationale for both the tremendous solvation of a Na⊕ center coordinated to seven oxygen centers of 15-crown-5 and of one diglyme molecule and the structural changes as well as the charge distribution in the unique Tetraphenyl-p-quinodimethane dianion (H5C6)2C⊖-(C6H4)- ⊖C(C6H5)2, in which the two negative charges are largely localized at the carbanion center of the benzene -substituents.
The structures of seven di- or tetrasubstituted p-benzoquinone derivatives O=C(XC=CH )2C=O and O=C(XC=CX)2C=O with substituents X = -OCH3, -N(CH2)5, - N(CH2CH2)2O, -Cl, -CN and -⊕N(HC=CH)2C-N(CH3)2 are presented and discussed in comparison with published ones substituted by X = -Si(CH3)3, -C6H5, -N(CH3)2, -⊕N(HC=CH)2CN(CH3)2, -O⊖ , and - NO2. Based on the introduction, in which halfwave-reduction potentials, geometry-optimized quantum-chemical calculations on substituent perturbation and known structural data of p-benzoquinone derivatives are used to characterize their molecular ground states. The structural changes indicate how substituent perturbations might be rationalized. Of the categories defined - imperturbed, donor, donor/acceptor and acceptor perturbed - the donorsubstituted p-benzoquinones do exhibit the largest differences, often called cyanine distorsion. In very satisfactory agreement with extensive semiempirical calculations, all effects determined experimentally are discussed in terms of varying charge distribution. With respect to the biochemical importance of p-benzoquinone derivatives, this first structural summary points out important facets.
The following mixed-stack donor/acceptor complexes {D · · · A }∞ have been crystallized and their structures determined: { 1 ,2,4,5-tetramethylbenzene · · · tetrabromo-p -benzoquinone}∞ , {hexamethylbenzene · · · tetrabromo-p-benzoquinone}∞ , { ( 1 ,2 ,4,5-tetramethyl-benzene)2 · · · tetrachloro -p -benzoquinone}∞ , {pyrene · · · tetrafluoro-p-benzoquinone}∞ , {pyrene · · · tetrabromo-p-benzoquinone}∞ and {perylene · · · tetrabromo-p-benzoquinone}∞ . They exhibit an interesting lattice packing, especially the 2:1 tripeldecker sandwich of tetrachloro-p-benzoquinone, which crystallizes in a herringbone pattern. Their interplanar distances are around 340 pm, i. e. two van der Waals π radii. None of them , however, exhibits in neither the donor nor the acceptor components significant structural changes due to complex formation. Their colours range from orange-red to black in the crystal and to green in H2CCl2 solution. Their long-wavelengths charge transfer absorption maxim a correspond to a lowering in excitation energy of up to 2 eV relative to that of the components. The different charge transfer in the ground and excited states of the donor/acceptor complexes investigated is further discussed referring to data such as cyclovoltammetric reduction potentials as w ell as to results from semiempirical calculations based on the crystal structure data determined and including configuration interaction.
Bis(N,N-diethyl-N′-benzoylselenoureato)lead(II) has been prepared and characterized by single-crystal structure analysis. Pb(C12H15N2OSe)2 crystallizes in the non-centrosymmetric orthorhombic space group Iba2. The cell parameters are a = 13.206(3), b = 20.542(4), c = 10.089(2) A and Z = 4. R = 0.025. The direction of the polar axis was determined unambig uously. Pb(II) is bidentally coordinated to two N,N-diethyl-N′-benzoylselenourea molecules. The coordination polyhedron is a distorted pseudo-trigonal bi-pyramid with one equatorial position occupied by an electron lone-pair. The Pb-Se and Pb-O bond lengths are 2.876(1) and 2.444(4) Å, respectively. In the crystal lattice, each Pb atom also shows interactions with two Se atoms of a neighboring molecule. The Pb-Se distance of that interaction is 3.643 Å.
Trimethylbromosilane and 3,4-lutidine form a 1:1 compound which is stable at room temperature. Single crystals of this compound can be isolated by sublimation. It crystallizes in the orthorhombic space group P 2121,21, with lattice constants a = 737,08(9) pm, b = 1295,7(1) pm, c = 1318,8(3) pm. The crystal structure was refined to Rw = 0,042 and proves an ionic structure.
Kristallstruktur von 1,1-Dichlor-3,5-diphenyl-4-H-1,2,4,6-λ4-selenatriazin, SeCl2C2N3H(C6H5)2
(1989)
The title compound has been prepared as a byproduct of the reaction of Se2Cl2 with Ν,Ν,N′-Tris(trimethylsilyl)benzamidine in CH2Cl2 solution. [SeCl2(HNC2N2Ph2)]2 was characterized by an X-ray structure determination. Space group P21/n, Z = 2, 2979 observed independent reflexions, R = 0.032. Lattice dimensions (-65 °C): a = 1050.1(4), b = 1018.9(4), c = 1402.1(6) pm; β = 99.78(3)°. The compound forms centrosymmetric dimeric molecules with SeCl2Se bridges (bond lengths 241.6(1) and 339.3(1) pm), the selenium atoms being members of nearly planar [xxx] selenatriazine rings with Se—N bond lengths of 182.2(2) and 181.5(2) pm.
[Na-15-crown-5][WF5(NCl)] has been prepared as yellow crystals by the reaction of NaF with WC14(NCl) in the presence of 15-crown-5 in acetonitrile solution. The compound was characterized by its IR spectrum as well as by an X-ray structure determination. Crystal data: space group P 21/n, Z = 4 (2945 observed, independent reflexions, R = 0.035). Lattice dimensions at - 65 °C: a = 827.2(8); b = 1617.3(13); c = 1372.2(10) pm; β = 99.42(5)°. The com pound forms ion pairs, in which the sodium ion is seven-coordinated by the oxygen atoms of the crown ether m olecule, and by two fluorine ligands of the [WF5(NCl)]- unit with Na -F distances of 228.3(6) and 251.3(6) pm. The W ≡ N-Cl group of the anion is nearly linear (bond angle 176.1(5)°) with bond lengths WN = 173.3(6) and NCI = 162.2(7) pm.
The title compound has been prepared by the reaction of N,N,N′-tris(trimethylsilyl)benzamidine with tantalum pentachloride in CH2Cl2 suspension, forming amber-coloured, moisturesensitive crystals, which were characterized by an X-ray structure determination. Space group P 21/n, Z = 2, 4895 observed independent reflexions, R = 0.059. Lattice dimensions (-65°C): a = 1165.2(6), b = 1335.4(6), c = 1629.0(7) pm, β = 93.23(4)°. The complex forms centrosymmetric molecules dimerized via chloro bridges TaCl2Ta with TaCl bond lengths of 247.2(2) and 277.1(2) pm, the longer one being in trans-position to the imido group, which can be formulated as [xxx] (bond lengths Ta=Ν = 183.5(8), C=N = 134(1) pm, bond angle TaNC = 162.7(7)°).