1q3k
From Proteopedia
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Crystal structure of creatinine amidohydrolase (creatininase)
Overview
Creatinine amidohydrolase (creatininase; EC 3.5.2.10) from Pseudomonas, putida, a homohexameric enzyme with a molecular mass of 28.4 kDa per, subunit, is a cyclic amidohydrolase catalysing the reversible conversion, of creatinine to creatine. The enzyme plays a key role in the bacterial, degradation of creatinine. The three-dimensional structure of creatininase, from P.putida was determined and refined to 2.1A. The structure shows the, six subunits arranged as a trimer of dimers and definitely disproves, previous reports that the enzyme has an octameric quaternary structure., Each monomer consists of a central, four-stranded, parallel beta-sheet, flanked by two alpha-helices on both sides of the beta-sheet. This, topology is unique within the superfamily of amidohydrolases. Moreover, creatininase possesses a novel fold with no close structural relatives, within the Protein Data Bank. Each creatininase monomer contains a, binuclear zinc centre near the C termini of the beta-strands and the N, termini of the main alpha-helices. These zinc ions indicate the location, of the active site unambiguously. The active site is entirely buried and, is not accessible from the solution without movement of parts of the, protein. The two zinc ions are bridged by a water molecule and by an, aspartate residue, which acts as a bidentate ligand. They differ from each, other in the number and the spatial arrangement of their ligands. One of, them is tetrahedrally and the other trigonal-bipyramidally ligated. Using, two water molecules of the first coordination sphere as anchor points, a, creatinine-water adduct resembling the transition state of the, hydrolysation reaction was modelled into the active site. The resulting, complex in combination with structural comparisons with other, amidohydrolases enabled us to identify the most probable candidate for the, catalytic base and to suggest a putative reaction mechanism. Surprisingly, these structural comparisons revealed a similarity in the active-site, arrangement between creatininase and the hydantoinase-like cyclic, amidohydrolases that was unexpected, given the completely unrelated, primary and tertiary structures. In particular, the zinc-bridging, aspartate residue of creatininase is a spatially and functionally analogue, to a carboxylated lysine residue found in dihydroorotase and the, hydantoinases. Hence, creatininase and the hydantoinase-like cyclic, amidohydrolases represent a further example of convergent evolution within, the enzyme class of hydrolases.
About this Structure
1Q3K is a Single protein structure of sequence from Pseudomonas putida with ZN and GOL as ligands. Active as Creatininase, with EC number 3.5.2.10 Full crystallographic information is available from OCA.
Reference
Crystal structure of creatininase from Pseudomonas putida: a novel fold and a case of convergent evolution., Beuth B, Niefind K, Schomburg D, J Mol Biol. 2003 Sep 5;332(1):287-301. PMID:12946365
Page seeded by OCA on Sun Nov 25 03:30:53 2007
