Enzymological and structural characterization of Arabidopsis thaliana heme oxygenase‐1

Abstract

Arabidopsis thaliana heme oxygenase‐1 (AtHO‐1), a metabolic enzyme in the heme degradation pathway, serves as a prototype for study of the bilin‐related functions in plants. Past biological analyses revealed that AtHO‐1 requires ferredoxin‐NADP + reductase (FNR) and ferredoxin for its enzymatic activity. Here, we characterized the binding and degradation of heme by AtHO‐1, and found that ferredoxin is a dispensable component of the reducing system that provides electrons for heme oxidation. Furthermore, we reported the crystal structure of heme‐bound AtHO‐1, which demonstrates both conserved and previously undescribed features of plant heme oxygenases. Finally, the electron transfer pathway from FNR to AtHO‐1 is suggested based on the known structural information.

Proximity labelling allows to study novel factors in chloroplast developmenta

“…Interestingly, EMB3119 has also been described as thioredoxin interacting protein (Marchand et al, 2006), which would provide an interesting link to CBSX2 in redox regulation (Yoo et al, 2011). GUN2 encodes a heme-oxygenase (Wang et al, 2022) necessary for coupling the expression of certain nuclear genes to the functional state of the chloroplast (Mochizuki et al, 2001). The six remaining proteins belong all to the RNA binding protein family.…”

Malaria parasites require a divergent heme oxygenase for apicoplast gene expression and biogenesis

“…We note that ordered, coiled loops were observed at the C-terminal end of the proximal helix in recent structures of plant HOs 24,25 (Figure 1 -figure supplement 4). Nevertheless, disorder in the C-terminal region of the proximal helix has previously been described in a structure of human HO1 bound to synthetic 5-phenylheme (where the 5-phenyl substituent sterically disrupts proximal helix structure near the αmeso carbon) and a structure of apo rat HO1 that lacked bound heme 26,27 .…”

“…In contrast to the ordered distal helix, we were unable to resolve the structure of the C-terminal region of the proximal helix (residues 112-133) of PfHO due to weak electron density for these residues, possibly reflecting static or dynamic structural disorder in this region. We note that ordered, coiled loops were observed at the C-terminal end of the proximal helix in recent structures of plant HOs 24,25 ( Figure 1 – figure supplement 4 ). Nevertheless, disorder in the C-terminal region of the proximal helix has previously been described in a structure of human HO1 bound to synthetic 5-phenylheme (where the 5-phenyl substituent sterically disrupts proximal helix structure near the α-meso carbon) and a structure of apo rat HO1 that lacked bound heme 26,27 .…”