Effect of the methionine ligand on the reorganization energy of the type-1 copper site of nitrite reductase.
Copper-containing nitrite reductase harbors a type-1 and a type-2 Cu site. The former acts as the electron acceptor site of the enzyme, and the latter is the site of catalytic action. The effect of the methionine ligand on the reorganization energy of the type-1 site was explored by studying the electron-transfer kinetics between NiR (wild type (wt) and the variants Met150Gly and Met150Thr) with Fe(II)EDTA and Fe(II)HEDTA. The mutations increased the reorganization energy by 0.3 eV (30 kJ mol-1). A similar increase was found from pulse radiolysis experiments on the wt NIR and three variants (Met150Gly, Met150His, and Met150Thr). Binding of the nearby Met62 to the type-1 Cu site in Met150Gly (under influence of an allosteric effector) lowered the reorganization energy back to approximately the wt value. According to XRD data the structure of the reduced type-1 site in Met150Gly NiR in the presence of an allosteric effector is similar to that in the reduced wt NiR (solved to 1.85 A), compatible with the similarity in reorganization energy.
Wijma
Hein J
HJ
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
MacPherson
Iain
I
Farver
Ole
O
Tocheva
Elitza I
EI
Pecht
Israel
I
Verbeet
Martin Ph
MP
Murphy
Michael E P
ME
Canters
Gerard W
GW
D001665:Binding Sites; D020134:Catalytic Domain; D002614:Chelating Agents / Q000737:chemistry; D004492:Edetic Acid / Q000031:analogs & derivatives; D004579:Electron Transport; D005998:Glycine / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D008715:Methionine / Q000737:chemistry*; D009154:Mutation; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation
D002614:Chelating Agents; D008024:Ligands; D004492:Edetic Acid; D008715:Methionine; D007501:Iron; D009572:Nitrite Reductases; C052695:nitrite reductase, copper-containing; D005998:Glycine