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Deacetoxycephalosporin-C synthase (DAOCS) is a mononuclear ferrous enzyme that transforms penicillins into cephalosporins by inserting a carbon atom into the penicillin nucleus. In the first half-reaction, dioxygen and 2-oxoglutarate produce a reactive iron-oxygen species, succinate and CO2. The oxidizing iron species subsequently reacts with penicillin to give cephalosporin and water. Here we describe high-resolution structures for ferrous DAOCS in complex with penicillins, the cephalosporin product, the cosubstrate and the coproduct. Steady-state kinetic data, quantum-chemical calculations and the new structures indicate a reaction sequence in which a 'booby-trapped' oxidizing species is formed. This species is stabilized by the negative charge of succinate on the iron. The binding sites of succinate and penicillin overlap, and when penicillin replaces succinate, it removes the stabilizing charge, eliciting oxidative attack on itself. Requisite groups of penicillin are within 1 A of the expected position of a ferryl oxygen in the enzyme-penicillin complex.

Ab initio calculations on a linear –OTiOTiO– chain embedded in an envelope of (SiO4) tetrahedra, mimicking the structure of Na2TiSi5O13 molecular sieve (ETS-10), confirm that the peculiar optical properties of the solid are associated with the presence of –OTiOTiO– linear chains behaving as quantum wires. The optical [in the UV-Vis (ultraviolet-range)] and the magnetic [(ESR) electron spin resonance] properties of these chains can be modified by adsorbing Na vapors. The sodium atoms diffusing into the channels undergo a ionization process with formation of Na+ (localized in the main channels) and Ti3+ (in the –OTiOTiO– chain, which so becomes a nonstoichiometric wire) characterized by Ti/Na ratios in the 2–4 range. Successive adsorption of oxygen at room temperature leads to the partial (Ti/Na∼2) or total (Ti/Na∼4) restoration of the chain stoichiometry and to the predominant formation of sodium oxide. The formation of a minor fraction of superoxide negative ions whose magnetic properties are revealed by ESR spectroscopy is also observed. Total restoration of the optical properties of the original samples is always obtained when the oxygen adsorption is made at 473 K. The sample keeps its structural integrity during the reduction and successive oxidation process.

No abstract

Background: GPR17 is a G-protein-coupled receptor located at intermediate phylogenetic position between two distinct receptor families: the P2Y and CysLT receptors for extracellular nucleotides and cysteinyl-LTs, respectively. We previously showed that GPR17 can indeed respond to both classes of endogenous ligands and to synthetic compounds active at the above receptor families, thus representing the first fully characterized non-peptide "hybrid" GPCR. In a rat brain focal ischemia model, the selective in vivo knock down of GPR17 by anti-sense technology or P2Y/ CysLT antagonists reduced progression of ischemic damage, thus highlighting GPR17 as a novel therapeutic target for stroke. Elucidation of the structure of GPR17 and of ligand binding mechanisms are the necessary steps to obtain selective and potent drugs for this new potential target. On this basis, a 3-D molecular model of GPR17 embedded in a solvated phospholipid bilayer and refined by molecular dynamics simulations has been the first aim of this study. To explore the binding mode of the "purinergic" component of the receptor, the endogenous agonist UDP and two P2Y receptor antagonists demonstrated to be active on GPR17 (MRS2179 and cangrelor) were then modeled on the receptor.