1e2r

File:1e2r.gif

CYTOCHROME CD1 NITRITE REDUCTASE, REDUCED AND CYANIDE BOUND

Overview

We present a 1.59-A resolution crystal structure of reduced Paracoccus pantotrophus cytochrome cd(1) with cyanide bound to the d(1) heme and His/Met coordination of the c heme. Fe-C-N bond angles are 146 degrees for the A subunit and 164 degrees for the B subunit of the dimer. The nitrogen atom of bound cyanide is within hydrogen bonding distance of His(345) and His(388) and either a water molecule in subunit A or Tyr(25) in subunit B. The ferrous heme-cyanide complex is unusually stable (K(d) approximately 10(-6) m); we propose that this reflects both the design of the specialized d(1) heme ring and a general feature of anion reductases with active site heme. Oxidation of crystals of reduced, cyanide-bound, cytochrome cd(1) results in loss of cyanide and return to the native structure with Tyr(25) as a ligand to the d(1) heme iron and switching to His/His coordination at the c-type heme. No reason for unusually weak binding of cyanide to the ferric state can be identified; rather it is argued that the protein is designed such that a chelate-based effect drives displacement by tyrosine of cyanide or a weaker ligand, like reaction product nitric oxide, from the ferric d(1) heme.

About this Structure

1E2R is a Single protein structure of sequence from Paracoccus denitrificans. Full crystallographic information is available from OCA.

Reference

X-ray crystallographic study of cyanide binding provides insights into the structure-function relationship for cytochrome cd1 nitrite reductase from Paracoccus pantotrophus., Jafferji A, Allen JW, Ferguson SJ, Fulop V, J Biol Chem. 2000 Aug 18;275(33):25089-94. PMID:10827177 Page seeded by OCA on Fri May 2 14:35:14 2008

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