1xdu
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(New page: 200px<br /><applet load="1xdu" size="450" color="white" frame="true" align="right" spinBox="true" caption="1xdu, resolution 2.70Å" /> '''Crystal structure of...)
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Revision as of 23:49, 24 November 2007
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Crystal structure of Aclacinomycin-10-hydroxylase (RdmB) in complex with Sinefungin (SFG)
Overview
Aclacinomycin 10-hydroxylase is a methyltransferase homologue that, catalyzes a S-adenosyl-L-methionine (AdoMet)-dependent hydroxylation of, the C-10 carbon atom of 15-demethoxy-epsilon-rhodomycin, a step in the, biosynthesis of the polyketide antibiotic beta-rhodomycin., S-Adenosyl-L-homocysteine is an inhibitor of the enzyme, whereas the, AdoMet analogue sinefungin can act as cofactor, indicating that a positive, charge is required for catalysis. 18O2 experiments show that the hydroxyl, group is derived from molecular oxygen. The reaction further requires, thiol reagents such as glutathione or dithiothreitol. Incubation of the, enzyme with substrate in the absence of reductant leads to the, accumulation of an intermediate with a molecular mass consistent with a, perhydroxy compound. This intermediate is turned into product upon, addition of glutathione. The crystal structure of an abortive, enzyme-AdoMet product ternary complex reveals large conformational changes, consisting of a domain rotation leading to active site closure upon, binding of the anthracycline ligand. The data suggest a mechanism where, decarboxylation of the substrate results in the formation of a carbanion, intermediate, which is stabilized by resonance through the aromatic ring, system of the anthracycline substrate. The delocalization of the electrons, is facilitated by the positive charge of the cofactor AdoMet. The, activation of oxygen and formation of a hydroxyperoxide intermediate, occurs in a manner similar to that observed in flavoenzymes., Aclacinomycin-10-hydroxylase is the first example of a AdoMet-dependent, hydroxylation reaction, a novel function for this cofactor. The enzyme, lacks methyltransferase activity due to the positioning of the AdoMet, methyl group unfavorable for a SN2-type methyl transfer to the substrate.
About this Structure
1XDU is a Single protein structure of sequence from Streptomyces purpurascens with ACT and SFG as ligands. Full crystallographic information is available from OCA.
Reference
Aclacinomycin 10-hydroxylase is a novel substrate-assisted hydroxylase requiring S-adenosyl-L-methionine as cofactor., Jansson A, Koskiniemi H, Erola A, Wang J, Mantsala P, Schneider G, Niemi J, J Biol Chem. 2005 Feb 4;280(5):3636-44. Epub 2004 Nov 17. PMID:15548527
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