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Hydrogen peroxide‐mediated conversion of coproheme to heme b by HemQ—lessons from the first crystal structure and kinetic studies
Author(s) -
Hofbauer Stefan,
Mlynek Georg,
Milazzo Lisa,
Pühringer Dominic,
Maresch Daniel,
Schaffner Irene,
Furtmüller Paul G.,
Smulevich Giulietta,
DjinovićCarugo Kristina,
Obinger Christian
Publication year - 2016
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.13930
Subject(s) - chemistry , heme , propionate , decarboxylation , stereochemistry , ferric , resonance raman spectroscopy , propionates , hydrogen bond , crystal structure , molecule , crystallography , organic chemistry , raman spectroscopy , enzyme , catalysis , physics , optics
Heme biosynthesis in Gram‐positive bacteria follows a recently described coproporphyrin‐dependent pathway with HemQ catalyzing the decarboxylation of coproheme to heme b . Here we present the first crystal structure of a HemQ (homopentameric coproheme‐HemQ from Listeria monocytogenes ) at 1.69 Å resolution and the conversion of coproheme to heme b followed by UV ‐vis and resonance Raman spectroscopy as well as mass spectrometry. The ferric five‐coordinated coproheme iron of HemQ is weakly bound by a neutral proximal histidine H174. In the crystal structure of the resting state, the distal Q187 (conserved in Firmicutes HemQ) is H‐bonded with propionate p2 and the hydrophobic distal cavity lacks solvent water molecules. Two H 2 O 2 molecules are shown to be necessary for decarboxylation of the propionates p2 and p4, thereby forming the corresponding vinyl groups of heme b . The overall reaction is relatively slow ( k cat / K M = 1.8 × 10 2 m −1 ·s −1 at pH 7.0) and occurs in a stepwise manner with a three‐propionate intermediate. We present the noncovalent interactions between coproheme and the protein and propose a two‐step reaction mechanism. Furthermore, the structure of coproheme‐HemQ is compared to that of the phylogenetically related heme b ‐containing chlorite dismutases. Database Structural data are available in the PDB under the accession number 5LOQ .