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. 2016 Oct 11;52(83):12286-12289.
doi: 10.1039/c6cc07004c.

In situ formation of the first proteinogenically functionalized [TeW6O24O2(Glu)]7- structure reveals unprecedented chemical and geometrical features of the Anderson-type cluster

Christian Molitor  1 , Aleksandar Bijelic  1 , Annette Rompel  1
Affiliations

In situ formation of the first proteinogenically functionalized [TeW6O24O2(Glu)]7- structure reveals unprecedented chemical and geometrical features of the Anderson-type cluster

Christian Molitor et al. Chem Commun (Camb). .

Abstract

The chemistry of polyoxometalates (POMs) in a protein environment is an almost unexplored but highly relevant research field as important biological and pharmacological attributes of certain POMs are based on their interactions with proteins. We report on the A-type Anderson-Evans polyoxotungstate, [TeW6O24]6- (TEW), mediated crystallization of Coreopsis grandiflora aurone synthase (cgAUS1) using ∼0.24 mM protein and 1.0 mM TEW. The 1.78 Å crystal structure reveals the covalent binding of TEW to the protein under the formation of an unprecedented polyoxotungstate cluster, [TeW6O24O2(Glu)]7- (GluTEW). The polyoxotungstate-protein complex exhibits the first covalent bond between a protein and the A-type Anderson-Evans cluster, an archetype where up to now no hybrid structures exist. The polyoxotungstate is modified at two of its six addenda tungsten atoms, which covalently bind to the carboxylic oxygen atoms of glutamic acid (Glu157), leading to W-O distances of ∼2.35 Å. This ligand substitution reaction is accompanied by a reduction of the coordination number of two μ3 polyoxotungstate oxygen atoms. This is so far unique since all known hybridizations of the Anderson-Evans POM with organic units have been obtained via the functionalization of the B-type Anderson-Evans structure through its bridging oxygen atoms. The structure reported here proves the reactivity of this POM archetype's addenda atoms as it has been administered into the protein solution as a pre-assembled cluster. Moreover, the novel cluster [TeW6O24O2(Glu)]7- displays the great versatility of the Anderson-Evans POM class.

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Figures

Fig. 1
Fig. 1. Asymmetric unit of CrystTEW and electrostatic potential of the binding pockets of GluTEW and TEW. (a) Representation of the asymmetric unit of CrystTEW. The interfacing GluTEW and TEW are presented as magenta spheres. The third chain B* was omitted for clarity. (b) GluTEW and TEW bind to a positively charged cleft and a patch, respectively. The molecular surface of the monomers is colored by the electrostatic potential on the solvent accessible surface (scale in kT e–1). Left: GluTEW binds within the interface of three cgAUS1 monomers. The symmetry related chain B* is visualized in cartoon/stick representation. Right: Binding site of TEW.
Fig. 2
Fig. 2. Covalent binding of GluTEW resulting in a novel polyoxotungstate. (a) Left: The carboxylic oxygen atoms of Glu157 bind covalently to two tungsten atoms of hexatungstotellurate(vi) (W–O distance ∼2.35 Å), while a reduction of the coordination number of two tridentate oxygen atoms occurs. A partially 2Fo–Fc electron density map (blue mesh) contoured at 1.0σ is shown. Right: Structure comparison of TEW, GluTEW and the polyoxomolybdate [Ag2IMo6O24]3–. (b) Analysis of GluTEW–protein interactions using LigPlot+. Left: Direct TEW–cgAUS1 hydrogen interactions. Right: Water-mediated TEW–cgAUS1 hydrogen interactions. Color code: (a) ball-and-stick presentation: carbon, light-cyan; nitrogen, blue; oxygen, red; tungsten, black; tellurium, grey. Polyhedra presentation: carbon, green; nitrogen, blue; oxygen, red; tungsten, marine-blue; tellurium, light-brown; silver, gold; molybdenum, forest-green; iodine, purple. (b) Small sphere presentation: carbon, green; nitrogen, blue; oxygen, red; tungsten, black; tellurium, grey; water molecules, light-cyan.
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