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The alkylsulfatase AtsK from Pseudomonas putida S-313 is a member of the non-heme iron(II)-␣-ketoglutarate-dependent dioxygenase superfamily. In the initial step of their catalytic cycle, enzymes belonging to this widespread and versatile family coordinate molecular oxygen to the iron center in the active site. The subsequent decarboxylation of the cosubstrate ␣-ketoglutarate yields carbon dioxide, succinate, and a highly reactive ferryl (IV) species, which is required for substrate oxidation via a complex mechanism involving the transfer of radical species. Non-productive activation of oxygen may lead to harmful side reactions; therefore, such enzymes need an effective built-in protection mechanism. One of the ways of controlling undesired side reactions is the self-hydroxylation of an aromatic side chain, which leads to an irreversibly inactivated species. Here we describe the crystal structure of the alkylsulfatase AtsK in complexes with succinate and with Fe(II)/succinate. In the crystal structure of the AtsKFe(II)-succinate complex, the side chain of Tyr 168 is coordinated to the iron, suggesting that Tyr 168 is the target of enzyme self-hydroxylation. This is the first structural study of an Fe(II)-␣-ketoglutarate-dependent dioxygenase that presents an aromatic side chain coordinated to the metal center, thus allowing structural insight into this protective mechanism of enzyme self-inactivation.The alkylsulfatase AtsK from Pseudomonas putida S-313 is a member of the family of non-heme iron(II), ␣-ketoglutarate-dependent dioxygenases (1, 2). This remarkable superfamily is widespread among prokaryotic and eukaryotic organisms, and its members catalyze a broad diversity of energetically demanding biosynthetic and degradative reactions including hydroxylation processes, stereoselective desaturation of inactivated carbon-carbon single bonds, and oxidative ring closure (3). The catalytic mechanism of this enzyme superfamily has been the topic of numerous spectroscopic and structural investigations (Fig. 1). This family of enzymes all bind iron using a 2-His-1-carboxylate facial triad, a feature that is one of nature's recurring multifunctional bioinorganic motifs such as the heme group or iron-sulfur clusters. They catalyze the oxidative conversion of the cofactor ␣KG 1 into CO 2 and succinate, simultaneously generating an activated oxygen species bound to the oxidized Fe center.The generally accepted mechanism proceeds via a Fe(IV)-oxo intermediate (4). The interaction of this activated intermediate with the enzyme substrate generates a transient radical species that subsequently decomposes to the reaction product. A reaction mechanism that involves radical formation would at first sight seem to be a hazardous method for an organism to accomplish the relatively straightforward cleavage reaction that is catalyzed by AtsK (i.e. the release of sulfate from an alkyl sulfate ester), because harmful side reactions could take place in the absence of substrate. Such enzymes must therefore have an effective built-in pro...

An extensive characterization of Co3(PO4)2 was performed by topological analysis according to Bader‘s Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid‐state heterogeneous oxidative‐dehydration and ‐dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five‐ and sixfold‐coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d‐orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold‐coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C−H activation.

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Solid‐state catalysis is the most important sustainable principle in chemical production. It lowers energy consumption, avoids waste and in many cases even volatile organic compounds as solvents. Experimental charge density determination in combination with computational methods pave the way to discriminate inactive against active solid‐state surfaces and assign catalytically active sites. This work investigated Co3(PO4)2 and identified the (011) face to be best suited for catalysis. Five‐fold coordinated Co ions in close proximity to advantageously oriented electron depletion sites suit the reactant's oxygen‐lone pairs most for chemisorption and heterogeneous C−H activation. More information can be found in the Full Paper by D. Stalke et al. on page 15786.