Dataset Information

The heme regulatory motifs of heme oxygenase-2 function to transfer heme to the catalytic site for degradation

ABSTRACT: Heme regulatory motifs (HRMs) are found in a variety of proteins that are involved in diverse biological functions. In the C-terminal tail region of human heme oxygenase-2 (HO2), there are two HRMs whose cysteines form a disulfide bond; when reduced, these cysteines are available to bind Fe3+-heme. Heme binding to the HRMs is independent of the HO2 catalytic active site in the core of the protein, where heme binds with high affinity and is degraded to biliverdin. Here, we describe the reversible, protein-mediated transfer of heme between the HRMs and the core of HO2. Using HDX-MS to monitor the dynamics of HO2 with and without Fe3+-heme bound to the HRMs and to the core, we detected conformational changes in the catalytic core only in one state of the catalytic cycle – when Fe3+-heme is bound to the HRMs and the core is in the apo state. The conformational changes detected are consistent with transfer of heme between binding sites. Indeed, Fe3+-heme bound to the HRMs is transferred to the apo-core upon either independently expressing the core and a construct spanning the HRM-containing tail or after single turnover of heme at the core. In addition, we observed transfer of heme from the core to the HRMs and equilibration of heme between the core and HRMs. We thus propose a Fe3+-heme transfer model in which heme bound to the HRMs is readily transferred to the catalytic site for degradation to facilitate turnover but can also equilibrate between the sites to maintain heme homeostasis.

INSTRUMENT(S): Synapt MS

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: John R. Engen

LAB HEAD: John R Engen

PROVIDER: PXD017538 | Pride | 2020-03-18

REPOSITORIES: Pride

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The heme-regulatory motifs of heme oxygenase-2 contribute to the transfer of heme to the catalytic site for degradation.

Fleischhacker Angela S AS Gunawan Amanda L AL Kochert Brent A BA Liu Liu L Wales Thomas E TE Borowy Maelyn C MC Engen John R JR Ragsdale Stephen W SW

The Journal of biological chemistry 20200309 16

Heme-regulatory motifs (HRMs) are present in many proteins that are involved in diverse biological functions. The C-terminal tail region of human heme oxygenase-2 (HO2) contains two HRMs whose cysteine residues form a disulfide bond; when reduced, these cysteines are available to bind Fe<sup>3+</sup>-heme. Heme binding to the HRMs occurs independently of the HO2 catalytic active site in the core of the protein, where heme binds with high affinity and is degraded to biliverdin. Here, we describe ...[more]

PMID: 32152224

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Project description:After a bloodmeal, mosquitoes import heme into the midgut epithelium. Heme acts as an essential signal for oogenesis in Aedes aegypti. However, the mechanisms behind heme import in Aedes aegypti are largely unexplored. In this study, RNA sequencing data from 4 different Aedes aegypti cell culture experiments where exposure to an overabundance or deficiency of heme was examined to identify heme-responsive genes. Zinc mesoporphyrin (ZnMP), a heme fluorescent analog, was used to measure changes in heme uptake prior to mRNA sequencing. A soft cluster analysis was performed to identify genes encoding potential membrane bound importers and exporters based on expression profiles across the samples for each experiment. Stronger candidates were obtained by comparing genes in each dataset to each other. When comparing all datasets to each other, 223 candidate genes with expression pattern changes consistent with importers were found to be heme-regulated in only 2 datasets, 46 were heme-regulated in 3 datasets and 2 was heme-regulated in all 4 datasets. In contrast, 114 candidate genes with patterns consistent with exporters were common to only 2 datasets, with just 11 present in 3 of the 4 datasets. A large number of genes containing transmembrane domains were isolated across the 4 datasets which showed downregulation or upregulation in response to heme overexposure conditions indicating the possibility that heme membrane bound import and export genes were identified respectively, with the reverse trend observed in the presence of heme deficiency. However, few transporter candidate genes were identified that showed high differential expression (above 4-fold or below 1/4th fold). Ultimately, as few strong candidates were identified by these studies, we consider the possibility that each cell line could have a redundant system of heme import, whereby multiple transport proteins each contribute to the total heme accumulation in the cell. Alternatively, it is possible that these cells lines do not regulate heme transport at the transcript level, but rather do so post-translationally.

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