1otw
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(New page: 200px<br /><applet load="1otw" size="450" color="white" frame="true" align="right" spinBox="true" caption="1otw, resolution 2.30Å" /> '''Crystal structure of...)
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Revision as of 21:04, 20 November 2007
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Crystal structure of PqqC in complex with PQQ and a putative H2O2
Overview
The biosynthesis of pyrroloquinoline quinone (PQQ), a vitamin and redox, cofactor of quinoprotein dehydrogenases, is facilitated by an unknown, pathway that requires the expression of six genes, pqqA to -F. PqqC, the, protein encoded by pqqC, catalyzes the final step in the pathway in a, reaction that involves ring cyclization and eight-electron oxidation of, 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-d, icarboxylic-acid to PQQ. Herein, we describe the crystal structures of, PqqC and its complex with PQQ and determine the stoichiometry of H2O2, formation and O2 uptake during the reaction. The PqqC structure(s) reveals, a compact seven-helix bundle that provides the scaffold for a positively, charged active site cavity. Product binding induces a large conformational, change, which results in the active site recruitment of amino acid side, chains proposed to play key roles in the catalytic mechanism. PqqC is, unusual in that it transfers redox equivalents to molecular oxygen without, the assistance of a redox active metal or cofactor. The structure of the, enzyme-product complex shows additional electron density next to R179 and, C5 of PQQ, which can be modeled as O2 or H2O2, indicating a site for, oxygen binding. We propose a reaction sequence that involves, base-catalyzed cyclization and a series of quinone-quinol tautomerizations, that are followed by cycles of O2/H2O2-mediated oxidations.
About this Structure
1OTW is a Single protein structure of sequence from Klebsiella pneumoniae with PQQ and PEO as ligands. Full crystallographic information is available from OCA.
Reference
Quinone biogenesis: Structure and mechanism of PqqC, the final catalyst in the production of pyrroloquinoline quinone., Magnusson OT, Toyama H, Saeki M, Rojas A, Reed JC, Liddington RC, Klinman JP, Schwarzenbacher R, Proc Natl Acad Sci U S A. 2004 May 25;101(21):7913-8. Epub 2004 May 17. PMID:15148379
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