PDBsum entry 2hq2

Oxidoreductase

PDB id: 2hq2

Contents

Protein chain

331 a.a. *

Ligands

HEM

Waters ×455

* Residue conservation analysis

Superseded by:

4cdp

PDB id:

2hq2

Name:

Oxidoreductase

Title:

Structure of the escherichia coli o157:h7 heme oxygenase chus in complex with heme

Structure:

Putative heme/hemoglobin transport protein. Chain: a. Synonym: hypothetical protein ecs4379. Engineered: yes

Source:

Escherichia coli. Organism_taxid: 83334. Strain: o157:h7. Gene: chus. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

Resolution:

1.45Å R-factor: 0.171 R-free: 0.193

Authors:

M.D.L.Suits,N.Jaffer,Z.Jia,Montreal-Kingston Bacterial Structural Genomics Initiative (Bsgi)

Key ref:

M.D.Suits et al. (2006). Structure of the Escherichia coli O157:H7 heme oxygenase ChuS in complex with heme and enzymatic inactivation by mutation of the heme coordinating residue His-193. J Biol Chem, 281, 36776-36782. PubMed id: 17023414 DOI: 10.1074/jbc.M607684200

Date:

18-Jul-06 Release date: 10-Oct-06

Protein chain

Q8X5N8  (Q8X5N8_ECO57) -  Hemin transporter from Escherichia coli O157:H7

Seq: 342 a.a.

Struc: 331 a.a.

DOI no: 10.1074/jbc.M607684200

J Biol Chem 281:36776-36782 (2006)

PubMed id: 17023414

Structure of the Escherichia coli O157:H7 heme oxygenase ChuS in complex with heme and enzymatic inactivation by mutation of the heme coordinating residue His-193.

M.D.Suits, N.Jaffer, Z.Jia.

ABSTRACT

Heme oxygenases catalyze the oxidation of heme to biliverdin, CO, and free iron. For pathogenic microorganisms, heme uptake and degradation are critical mechanisms for iron acquisition that enable multiplication and survival within hosts they invade. Here we report the first crystal structure of the pathogenic Escherichia coli O157:H7 heme oxygenase ChuS in complex with heme at 1.45 A resolution. When compared with other heme oxygenases, ChuS has a unique fold, including structural repeats and a beta-sheet core. Not surprisingly, the mode of heme coordination by ChuS is also distinct, whereby heme is largely stabilized by residues from the C-terminal domain, assisted by a distant arginine from the N-terminal domain. Upon heme binding, there is no large conformational change beyond the fine tuning of a key histidine (His-193) residue. Most intriguingly, in contrast to other heme oxygenases, the propionic side chains of heme are orientated toward the protein core, exposing the alpha-meso carbon position where O(2) is added during heme degradation. This unique orientation may facilitate presentation to an electron donor, explaining the significantly reduced concentration of ascorbic acid needed for the reaction. Based on the ChuS-heme structure, we converted the histidine residue responsible for axial coordination of the heme group to an asparagine residue (H193N), as well as converting a second histidine to an alanine residue (H73A) for comparison purposes. We employed spectral analysis and CO measurement by gas chromatography to analyze catalysis by ChuS, H193N, and H73A, demonstrating that His-193 is the key residue for the heme-degrading activity of ChuS.

Selected figure(s)

Figure 1.
FIGURE 1. Ribbon diagram of ChuS in complex with heme. ChuS binds to heme in a cleft region delineated by the C-terminal half (green) and N-terminal half (slate) between His-193 at the base of an -helix and Arg-100 via two water molecules (blue) from a central set of -sheets at the core of ChuS. The residues important for heme coordination as well as the mutant control position His-73 are depicted in red. Inset, stick diagram of superimposed residues 178-205 of apo-ChuS (red) and ChuS-Heme (green). Side chains 192-195 are shown. The local root mean square deviation for these residues of the apo- and ligand-bound form of ChuS is 3.10 Å. Figs. 1 and 2 were generated using PyMOL.

Figure 2.
FIGURE 2. Difference omit map for the heme moiety and two water molecules (blue) within the active site pocket of ChuS contoured at 2 in the R[3] space group. Heme and waters were omitted from refinement prior to map calculations. Residues contributing to heme stabilization include the non-polar series Leu-90, Leu-92, Phe-102, Val-192, and Phe-243 and the polar series Arg-100, His-193, Arg-206, Met-241, Lys-291, Gln-313, Tyr-315, and Arg-318. Heme is therefore mainly coordinated by the C-terminal half but also by a distant residue, Arg-100 from the N-terminal half. A network of hydrogen bonds is formed between Arg-100 and the iron atom of the heme group via two water molecules (dotted lines). In this orientation, the propionic side chains of the heme group point toward the protein interior, exposing the -meso carbon edge (black arrow). This presentation of the -meso edge may facilitate electron attack during heme degradation.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2006, 281, 36776-36782) copyright 2006.

Figures were selected by an automated process.