# Biochemical Mechanism of Mercury Methylation

> **NIH NIH R01** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2021 · $221,937

## Abstract

Project Summary/Abstract
Biochemical Mechanism of Mercury Methylation
 Our goal is to determine the biochemical mechanism of mercury (Hg) methylation, an
important contaminant transformation that occurs in hypoxic subsurface environments. We will
characterize HgcA and HgcB, the two proteins shown to be required for Hg methylation by
anaerobic microorganisms. In collaboration with the Oak Ridge National Laboratory (ORNL) Hg
Science Focus Area (SFA) program, we have produced HgcB containing high levels of its [4Fe-
4S] cofactor and a soluble cobalamin (Cbl) binding domain of HgcA. Recent work has led to the
following working hypotheses: (a) the two iron-sulfur clusters in HgcB receive electrons from a
low-potential oxidoreductase (pyruvate ferredoxin oxidoreductase, hydrogenase, CO
dehydrogenase, etc.); (b) HgcB transfers these reducing equivalents to the Cbl cofactor of
HgcA, converting it from Co(III) to the supernucleophilic Co(I) state; (c) Cys73 and the C-
terminal vicinal cysteine residues (Cys95 and Cys96 in Desulfovibrio desulfuricans ND132) of
HgcB bind Hg; and (d) HgcA catalyzes the methyltetrahydrofolate (CH3-H4folate)-dependent
methylation of the Co(I)-Cbl to generate methyl-Co(III) followed by transfer of the methyl group
of methyl-Co(III) to Hg(II) producing MeHg. Our two experimental objectives are to: (1)
characterize the structure and function of HgcB and examine its roles as a Hg carrier and redox
partner to HgcA and PFOR and (2) characterize the interactions and the methylation reactions
involving HcgB and HgcA. Our experiments will use a wide variety of biophysical and
biochemical techniques allowing us to characterize the multidimensional roles of these proteins
in binding heavy metals, performing electron transfer reactions, and catalyzing methyl transfers,
ultimately generating a potent and toxic neurotoxin. The experiments include spectroscopy
(NMR, EPR, resonance Raman, etc.), kinetics (steady-state and transient), electrochemistry
and binding measurements (surface plasmon resonance, isothermal calorimetry, NMR, etc).
Our results will uncover the biochemical mechanism of MeHg production, revealing a
fundamental understanding of the novel methyl transfer reactions catalyzed by HgcA and HgcB.
This work will be generally relevant to the microbiological transformations of heavy metals. The
kinetic parameters will provide key input for metabolic and reactive transport models that can be
used by the ORNL group and others to predict Hg cycling from single organisms to ecosystems.
Thus, our work will help understand the processes that control the fate and transformation of Hg
in aquatic environments, which is important for mitigating risk to humans and ecosystems in
which these Hg-methylating organisms thrive.
 .

## Key facts

- **NIH application ID:** 10136632
- **Project number:** 5R01GM124174-04
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Stephen Wiley Ragsdale
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $221,937
- **Award type:** 5
- **Project period:** 2018-07-01 → 2022-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10136632

## Citation

> US National Institutes of Health, RePORTER application 10136632, Biochemical Mechanism of Mercury Methylation (5R01GM124174-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10136632. Licensed CC0.

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