1et7
From Proteopedia
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CRYSTAL STRUCTURE OF NITRITE REDUCTASE HIS255ASP MUTANT FROM ALCALIGENES FAECALIS S-6
Overview
Two active site residues, Asp-98 and His-255, of copper-containing nitrite, reductase (NIR) from Alcaligenes faecalis have been mutated to probe the, catalytic mechanism. Three mutations at these two sites (D98N, H255D, and, H255N) result in large reductions in activity relative to native NIR, suggesting that both residues are involved intimately in the reaction, mechanism. Crystal structures of these mutants have been determined using, data collected to better than 1. 9-A resolution. In the native structure, His-255 Nepsilon2 forms a hydrogen bond through a bridging water molecule, to the side chain of Asp-98, which also forms a hydrogen bond to a water, or nitrite oxygen ligated to the active site copper. In the D98N mutant, reorientation of the Asn-98 side chain results in the loss of the hydrogen, bond to the copper ligand water, consistent with a negatively charged, Asp-98 directing the binding and protonation of nitrite in the native, enzyme. An additional solvent molecule is situated between residues 255, and the bridging water in the H255N and H255D mutants and likely inhibits, nitrite binding. The interaction of His-255 with the bridging water, appears to be necessary for catalysis and may donate a proton to reaction, intermediates in addition to Asp-98.
About this Structure
1ET7 is a Single protein structure of sequence from Alcaligenes faecalis with CU and CD as ligands. Active as Nitrite reductase (NO-forming), with EC number 1.7.2.1 Full crystallographic information is available from OCA.
Reference
Catalytic roles for two water bridged residues (Asp-98 and His-255) in the active site of copper-containing nitrite reductase., Boulanger MJ, Kukimoto M, Nishiyama M, Horinouchi S, Murphy ME, J Biol Chem. 2000 Aug 4;275(31):23957-64. PMID:10811642
Page seeded by OCA on Tue Nov 20 14:17:44 2007
