2bbf
From Proteopedia
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Crystal structure of tRNA-guanine transglycosylase (TGT) from Zymomonas mobilis in complex with 6-amino-3,7-dihydro-imidazo[4,5-g]quinazolin-8-one
Overview
The bacterial tRNA-guanine transglycosylase (TGT) is a tRNA modifying, enzyme catalyzing the exchange of guanine 34 by the modified base preQ1., The enzyme is involved in the infection pathway of Shigella, causing, bacterial dysentery. As no crystal structure of the Shigella enzyme is, available the homologous Zymomonas mobilis TGT was used for, structure-based drug design resulting in new, potent, lin-benzoguanine-based inhibitors. Thorough kinetic studies show, size-dependent inhibition of these compounds resulting in either a, competitive or non-competitive blocking of the base exchange reaction in, the low micromolar range. Four crystal structures of TGT-inhibitor, complexes were determined with a resolution of 1.58-2.1 A. These, structures give insight into the structural flexibility of TGT necessary, to perform catalysis. In three of the structures molecular rearrangements, are observed that match with conformational changes also noticed upon tRNA, substrate binding. Several water molecules are involved in these, rearrangement processes. Two of them demonstrate the structural and, catalytic importance of water molecules during TGT base exchange reaction., In the fourth crystal structure the inhibitor unexpectedly interferes with, protein contact formation and crystal packing. In all presently known TGT, crystal structures the enzyme forms tightly associated homodimers, internally related by crystallographic symmetry. Upon binding of the, fourth inhibitor the dimer interface, however, becomes partially, disordered. This result prompted further analyses to investigate the, relevance of dimer formation for the functional protein. Consultation of, the available TGT structures and sequences from different species revealed, structural and functional conservation across the contacting residues., This suggests that bacterial and eukaryotic TGT could possibly act as, homodimers in catalysis. It is hypothesized that one unit of the dimer, performs the catalytic reaction whereas the second is required to, recognize and properly orient the bound tRNA for the catalytic reaction.
About this Structure
2BBF is a Single protein structure of sequence from Zymomonas mobilis with ZN and 344 as ligands. Active as Queuine tRNA-ribosyltransferase, with EC number 2.4.2.29 Full crystallographic information is available from OCA.
Reference
Crystal structures of tRNA-guanine transglycosylase (TGT) in complex with novel and potent inhibitors unravel pronounced induced-fit adaptations and suggest dimer formation upon substrate binding., Stengl B, Meyer EA, Heine A, Brenk R, Diederich F, Klebe G, J Mol Biol. 2007 Jul 13;370(3):492-511. Epub 2007 Apr 12. PMID:17524419
Page seeded by OCA on Wed Nov 21 08:41:47 2007
