1b15: Difference between revisions

Drosophila alcohol dehydrogenase (DADH) is an NAD+-dependent enzyme that, catalyzes the oxidation of alcohols to aldehydes/ketones. DADH is the, member of the short-chain dehydrogenases/reductases family (SDR) for which, the largest amount of biochemical data has been gathered during the last, three decades. The crystal structures of one binary form (NAD+) and three, ternary complexes with NAD+.acetone, NAD+.3-pentanone and, NAD+.cyclohexanone were solved at 2.4, 2.2, 1. 4 and 1.6 A resolution, respectively. From the molecular interactions observed, the reaction, mechanism could be inferred. The structure of DADH undergoes a, conformational change in order to bind the coenzyme. Furthermore, upon, binding of the ketone, a region that was disordered in the apo form, (186-191) gets stabilized and closes the active site cavity by creating, either a small helix (NAD+. acetone, NAD+.3-pentanone) or an ordered loop, (NAD+.cyclohexanone). The active site pocket comprises a hydrophobic, bifurcated cavity which explains why the enzyme is more efficient in, oxidizing secondary aliphatic alcohols (preferably R form) than primary, ones. Difference Fourier maps showed that the ketone inhibitor molecule, has undergone a covalent reaction with the coenzyme in all three ternary, complexes. Due to the presence of the positively charged ring of the, coenzyme (NAD+) and the residue Lys155, the amino acid Tyr151 is in its, deprotonated (tyrosinate) state at physiological pH. Tyr151 can subtract a, proton from the enolic form of the ketone and catalyze a nucleophilic, attack of the Calphaatom to the C4 position of the coenzyme creating an, NAD-ketone adduct. The binding of these NAD-ketone adducts to DADH, accounts for the inactivation of the enzyme. The catalytic reaction, proceeds in a similar way, involving the same amino acids as in the, formation of the NAD-ketone adduct. The p Kavalue of 9-9.5 obtained by, kinetic measurements on apo DADH can be assigned to a protonated Tyr151, which is converted to an unprotonated tyrosinate (p Ka7.6) by the, influence of the positively charged nicotinamide ring in the binary, enzyme-NAD+form. pH independence during the release of NADH from the, binary complex enzyme-NADH can be explained by either a lack of, electrostatic interaction between the coenzyme and Tyr151 or an apparent p, Kavalue for this residue higher than 10.0.

1B15 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Scaptodrosophila_lebanonensis Scaptodrosophila lebanonensis] with NAE as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Alcohol_dehydrogenase Alcohol dehydrogenase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.1.1.1 1.1.1.1] Structure known Active Sites: ACA, ACB, CAA, CAB, NA1, NA2, NA3, NB1, NB2 and NB3. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1B15 OCA].  

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