Browsing by Subject "X-ray crystallography"

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  • Hassan, Alaa A.; Mohamed, Nasr K.; El-Shaieb, Kamal M. A.; Tawfeek, Hendawy N.; Bräse, Stefan; Nieger, Martin (2019)
    2-Substituted hydrazinecarbothioamides and N ,2-disubstituted hydrazinecarbothioamides react in high yield with dimethyl acetylenedicarboxylate (DMAD) to give 4-oxo-Z-(thiazolidin-5-ylidene) acetate derivatives. Several mechanistic options involving interaction are presented. The structures of thiazolidin-4-ones have been unambiguously confirmed by single crystal X-ray crystallography. (C) 2014 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.
  • Takala, Heikki; Lehtivuori, Heli K.; Berntsson, Oskar; Hughes, Ashley; Nanekar, Rahul; Niebling, Stephan; Panman, Matthijs; Henry, Leocadie; Menzel, Andreas; Westenhoff, Sebastian; Ihalainen, Janne A. (2018)
    Phytochromes are photoreceptors in plants, fungi, and various microorganisms and cycle between metastable red light-absorbing (Pr) and far-red light-absorbing (Pfr) states. Their light responses are thought to follow a conserved structural mechanism that is triggered by isomerization of the chromophore. Downstream structural changes involve refolding of the so-called tongue extension of the phytochrome-specific GAF-related (PHY) domain of the photoreceptor. The tongue is connected to the chromophore by conserved DIP and PRXSF motifs and a conserved tyrosine, but the role of these residues in signal transduction is not clear. Here, we examine the tongue interactions and their interplay with the chromophore by substituting the conserved tyrosine (Tyr(263)) in the phytochrome from the extremophile bacterium Deinococcus radiodurans with phenylalanine. Using optical and FTIR spectroscopy, X-ray solution scattering, and crystallography of chromophore-binding domain (CBD) and CBD-PHY fragments, we show that the absence of the Tyr(263) hydroxyl destabilizes the -sheet conformation of the tongue. This allowed the phytochrome to adopt an -helical tongue conformation regardless of the chromophore state, hence distorting the activity state of the protein. Our crystal structures further revealed that water interactions are missing in the Y263F mutant, correlating with a decrease of the photoconversion yield and underpinning the functional role of Tyr(263) in phytochrome conformational changes. We propose a model in which isomerization of the chromophore, refolding of the tongue, and globular conformational changes are represented as weakly coupled equilibria. The results also suggest that the phytochromes have several redundant signaling routes.
  • Hassan, Alaa A.; Mohamed, Nasr K.; El-Shaieb, Kamal M. A.; Tawfeek, Hendawy N.; Bräse, Stefan; Nieger, Martin (2016)
    2-{Amino-[5-amino-2-(substituted diazenyl) thiazol-4-yl] methylene} malononitriles were synthesized from the reaction of 2-substituted hydrazinecarbothioamides with tetracyanoethylene (TCNE) to give tetracyanoethane adduct, followed by heterocyclization afforded the target compounds. The structure of (E)-2-{amino-[5-amino-2-(phenyldiazenyl) thiazol-4-yl] methylene} malononitrile was supported by single crystal X-ray crystallography.
  • Hassan, Alaa A.; Aly, Ashraf A.; Mohamed, Nasr K.; El-Shaieb, Kamal M.; Makhlouf, Maysa M.; Bräse, Stefan; Nieger, Martin; Brown, Alan B. (2020)
    The reaction between N-substituted alkenylidene hydrazinecarbothioamides and two molar amounts of tetracyanoethylene (TCNE) in anhydrous THF at room temperature without using any catalyst affords (Z)-4-amino-3-((Z)substituted amino)-2-(substituted imino)-2,3-dihydrothiazole-5-carbonitriles and (Z)-(4-amino-5-cyano-thiazol-2(3H)-ylidene)carbonhydrazonoyl dicyanides. Rationales for these transformations are presented. The structures of the obtained products were confirmed via single-crystal X-ray analyses. Graphic Here, we synthesize (Z)-4-amino-3-amino-2-imino-2,3-dihydrothiazole-5-carbonitriles and (Z)-(4-amino-5-cyano-thiazol-2(3H)-ylidene)carbonhydrazonoyl dicyanides from the reaction of N-substituted alkenylidene hydrazinecarbothioamides with (TCNE) in anhydrous THF at room temperature without using any catalyst. [GRAPHICS] .
  • Rissanen, Ilona; Stass, Robert; Zeltina, Antra; Li, Sai; Hepojoki, Jussi; Harlos, Karl; Gilbert, Robert J. C.; Huiskonen, Juha T.; Bowden, Thomas A. (2017)
    Hantaviruses are zoonotic pathogens that cause severe hemorrhagic fever and pulmonary syndrome. The outer membrane of the hantavirus envelope displays a lattice of two glycoproteins, Gn and Gc, which orchestrate host cell recognition and entry. Here, we describe the crystal structure of the Gn glycoprotein ectodomain from the Asiatic Hantaan virus (HTNV), the most prevalent pathogenic hantavirus. Structural overlay analysis reveals that the HTNV Gn fold is highly similar to the Gn of Puumala virus (PUUV), a genetically and geographically distinct and less pathogenic hantavirus found predominantly in northeastern Europe, confirming that the hantaviral Gn fold is architecturally conserved across hantavirus clades. Interestingly, HTNV Gn crystallized at acidic pH, in a compact tetrameric configuration distinct from the organization at neutral pH. Analysis of the Gn, both in solution and in the context of the virion, confirms the pH-sensitive oligomeric nature of the glycoprotein, indicating that the hantaviral Gn undergoes structural transitions during host cell entry. These data allow us to present a structural model for how acidification during endocytic uptake of the virus triggers the dissociation of the metastable Gn-Gc lattice to enable insertion of the Gc-resident hydrophobic fusion loops into the host cell membrane. Together, these data reveal the dynamic plasticity of the structurally conserved hantaviral surface. IMPORTANCE Although outbreaks of Korean hemorrhagic fever were first recognized during the Korean War (1950 to 1953), it was not until 1978 that they were found to be caused by Hantaan virus (HTNV), the most prevalent pathogenic hantavirus. Here, we describe the crystal structure of HTNV envelope glycoprotein Gn, an integral component of the Gn-Gc glycoprotein spike complex responsible for host cell entry. HTNV Gn is structurally conserved with the Gn of a genetically and geographically distal hantavirus, Puumala virus, indicating that the observed alpha/beta fold is well preserved across the Hantaviridae family. The combination of our crystal structure with solution state analysis of recombinant protein and electron cryo-microscopy of acidified hantavirus allows us to propose a model for endosome-induced reorganization of the hantaviral glycoprotein lattice. This provides a molecular-level rationale for the exposure of the hydrophobic fusion loops on the Gc, a process required for fusion of viral and cellular membranes.