Comparison of Apo- and Heme-bound Crystal Structures of a Truncated Human Heme Oxygenase-2

Li Yi,Christopher M Bianchetti,Stephen W Ragsdale,George N Phillips

doi:10.1074/jbc.m707396200

Abstract

Heme oxygenase (HO) catalyzes the first step in the heme degradation pathway. The crystal structures of apo- and heme-bound truncated human HO-2 reveal a primarily alpha-helical architecture similar to that of human HO-1 and other known HOs. Proper orientation of heme in HO-2 is required for the regioselective oxidation of the alpha-mesocarbon. This is accomplished by interactions within the heme binding pocket, which is made up of two helices. The iron coordinating residue, His(45), resides on the proximal helix. The distal helix contains highly conserved glycine residues that allow the helix to flex and interact with the bound heme. Tyr(154), Lys(199), and Arg(203) orient the heme through direct interactions with the heme propionates. The rearrangements of side chains in heme-bound HO-2 compared with apoHO-2 further elucidate HO-2 heme interactions.

Highlights

Heme oxygenase (HO)2 catalyzes the degradation of heme to free iron, carbon monoxide, and biliverdin in the presence of NADPH-dependent cytochrome P450 reductase
The two structures we present are of the core domain of human heme oxygenase-2 (HO-2)
In degradation, elucidating the important structural features of the same region that the unexplained density was found in HO-2 and improving our understanding of the catalytic mechheme-bound HO-2, a molecule of Triton X-100 was observed anism of HO-2

Summary

Introduction

Heme oxygenase (HO)2 catalyzes the degradation of heme to free iron, carbon monoxide, and biliverdin in the presence of NADPH-dependent cytochrome P450 reductase. We report the first apo- and heme- protein solution (50 mM KCl, 50 mM Tris-HCl, pH 7.5) mixed bound HO-2 crystal structures at 2.4- and 2.6-Å resolution, with 1.0 ␮l of well solution containing 40% polyethylene glycol respectively. Elongated positive electron density was observed near the heme in both molecules of the heme-bound HO-2 structure.

Results

Conclusion