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Updated: Feb 2, 2026
Characterizing Cellular Proteins with In-cell Fast Photochemical Oxidation of Proteins
Published on: March 11, 2020
MopA, the Mn Oxidizing Protein From Erythrobacter sp. SD-21, Requires Heme and NAD+ for Mn(II) Oxidation
Michael Medina1, Antonia Rizo1, David Dinh1
1Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States.
Abstract:
Bacterial manganese (Mn) oxidation is catalyzed by a diverse group of microbes and can affect the fate of other elements in the environment. Yet, we understand little about the enzymes that catalyze this reaction. The Mn oxidizing protein MopA, from Erythrobacter sp. strain SD-21, is a heme peroxidase capable of Mn(II) oxidation. Unlike Mn oxidizing multicopper oxidase enzymes, an understanding of MopA is very limited. Sequence analysis indicates that MopA contains an N-terminal heme peroxidase domain and a C-terminal calcium binding domain. Heterologous expression and nickel affinity chromatography purification of the N-terminal peroxidase domain (MopA-hp) from Erythrobacter sp. strain SD-21 led to partial purification. MopA-hp is a heme binding protein that requires heme, NAD+, and calcium (Ca2+) for activity. Mn oxidation is also stimulated by the presence of pyrroloquinoline quinone. MopA-hp has a K M for Mn(II) of 154 ± 46 μM and k cat = 1.6 min-1. Although oxygen requiring MopA-hp is homologous to peroxidases based on sequence, addition of hydrogen peroxide and hydrogen peroxide scavengers had little effect on Mn oxidation, suggesting this is not the oxidizing agent. These studies provide insight into the mechanism by which MopA oxidizes Mn.
Insights
Bacterial manganese oxidation is crucial for environmental element cycling. Researchers characterized MopA-hp, a heme peroxidase from Erythrobacter, revealing its requirements for Mn(II) oxidation and shedding light on its catalytic mechanism.
Area of Science:
- Environmental microbiology
- Biochemistry
- Enzyme kinetics
Background:
- Bacterial manganese oxidation influences environmental element cycling.
- The enzymes catalyzing manganese oxidation are poorly understood.
- MopA from Erythrobacter sp. strain SD-21 is a heme peroxidase involved in Mn(II) oxidation.
Purpose of the Study:
- To investigate the enzymatic mechanism of MopA-hp in bacterial manganese oxidation.
- To characterize the biochemical properties and requirements of the MopA-hp enzyme.
Main Methods:
- Sequence analysis of MopA.
- Heterologous expression and purification of the MopA N-terminal peroxidase domain (MopA-hp).
- Enzyme activity assays to determine kinetic parameters and cofactor requirements.
Main Results:
- MopA-hp requires heme, NAD+, and Ca2+ for Mn(II) oxidation activity.
- Pyrroloquinoline quinone stimulates Mn oxidation.
- Kinetic parameters: K_M = 154 ± 46 μM and k_cat = 1.6 min⁻¹.
- Hydrogen peroxide was not identified as the oxidizing agent despite sequence homology to peroxidases.
Conclusions:
- MopA-hp is a novel heme peroxidase catalyzing bacterial manganese oxidation.
- The enzyme's activity is dependent on specific cofactors and is not driven by hydrogen peroxide.
- This study provides critical insights into the mechanism of MopA-mediated manganese oxidation.
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