1dj5
From Proteopedia
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CRYSTAL STRUCTURE OF R48A MUTANT OF CYTOCHROME C PEROXIDASE WITH N-HYDROXYGUANIDINE BOUND
Overview
Heme enzymes are capable of catalyzing a range of oxidative chemistry with, high specificity, depending on the surrounding protein environment. We, describe here a reaction catalyzed by a mutant of cytochrome c peroxidase, which is similar but distinct from those catalyzed by nitric-oxide, synthase. In the R48A mutant, an expanded water-filled cavity was created, above the distal heme face. N-hydroxyguanidine (NHG) but not guanidine was, shown to bind in the cavity with K(d) = 8.5 mM, and coordinate to the heme, to give a low spin state. Reaction of R48A with peroxide produced a, Fe(IV)=O/Trp(.+) center capable of oxidizing either NHG or, N(omega)-hydroxyarginine (NHA), but not arginine or guanidine, by a, multi-turnover catalytic process. Oxidation of either NHG or NHA by R48A, did not result in the accumulation of NO, NO(2)(-), NO(3)(-), urea, or, citrulline, but instead afforded a yellow product with absorption maxima, of 257 and 400 nm. Mass spectrometry of the derivatized NHA products, identified the yellow species as N-nitrosoarginine. We suggest that a, nitrosylating agent, possibly derived from HNO, is produced by the, oxidation of one molecule of substrate. This then reacts with a second, substrate molecule to form the observed N-nitroso products. This complex, chemistry illustrates how the active sites of enzymes such as nitric-oxide, synthase may serve to prevent alternative reactions from occurring, in, addition to enabling those desired.
About this Structure
1DJ5 is a Single protein structure of sequence from Saccharomyces cerevisiae with HEM and HGU as ligands. Active as Cytochrome-c peroxidase, with EC number 1.11.1.5 Full crystallographic information is available from OCA.
Reference
Unusual oxidative chemistry of N(omega)-hydroxyarginine and N-hydroxyguanidine catalyzed at an engineered cavity in a heme peroxidase., Hirst J, Goodin DB, J Biol Chem. 2000 Mar 24;275(12):8582-91. PMID:10722697
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