Heme Ligation and Conformational Plasticity in the Isolatedc Domain of Cytochrome cd 1 Nitrite Reductase

Abstract

The heme ligation in the isolated c domain of Paracoccus pantotrophus cytochrome cd 1 nitrite reductase has been characterized in both oxidation states in solution by NMR spectroscopy. In the reduced form, the heme ligands are His

The Structure of an Alternative Form ofParacoccus pantotrophus Cytochromecd 1 Nitrite Reductase

“…Notably, the c heme iron is coordinated by His-69 and Met-106 in both structures. This is also the dominant structure in both oxidation states of the isolated cytochrome c domain (10). The large differences in relative domain arrangement seen in Fig.…”

“…A structure of the oxidized enzyme with His-Met ligation has indeed been anticipated (10,26). Allen et al (26) discovered that the enzyme in its as isolated oxidized form could not be reduced with one of its possible in vivo redox partners, pseudoazurin.…”

“…2, C and D), the interface between the two cytochrome c domains is stabilized mainly by hydrogen bonds via intervening solvent molecules. A recent study has shown that the isolated cytochrome c domain occurs as a monomer in solution (10), suggesting that the interactions between the c domains are relatively weak (Fig. 2).…”

“…Reduction also releases Tyr-25 from the d 1 heme in the active site, giving access to the iron for substrate binding. The His/Met ligation is a more common ligand combination in c-type cytochromes, and the isolated cytochrome c domain of NiR also adopts this heme ligation (10). Structural intermediates in nitrite reduction (4) and oxygen reduction (11) have been captured in the monoclinic crystals, and the structures of complexes between the reduced enzyme and carbon monoxide (6) and cyanide (CN Ϫ ) (12) have been determined.…”

Structure and Kinetic Properties of Paracoccus pantotrophus Cytochrome cd1 Nitrite Reductase with the d1 Heme Active Site Ligand Tyrosine 25 Replaced by Serine

“…Cytochrome cd 1 can act as an oxidase; and in the early stages of this reaction an oxidized state of the protein with His/Met coordination at the c-type cytochrome center has been observed (10,15), as was also the case for a form of the enzyme seen after a 1-electron oxidation of cytochrome cd 1 by nitrite (5). His/Met coordination of the heme of the c domain in the oxidized state is also found in solution for both the semi-apo form of the protein that has lost the d 1 heme (15) and the c domain expressed in isolation (16).…”