1e2r: Difference between revisions

[[Image:1e2r.gif|left|200px]]<br /><applet load="1e2r" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

1E2R is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Paracoccus_denitrificans Paracoccus denitrificans] with <scene name='pdbligand=CYN:'>CYN</scene>, <scene name='pdbligand=HEC:'>HEC</scene>, <scene name='pdbligand=DHE:'>DHE</scene> and <scene name='pdbligand=GOL:'>GOL</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1E2R OCA].  

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