Mercury is highly toxic, and its most dangerous form, methylmercury, can cause severe neurological damage, even in tiny amounts, especially to developing fetuses. Methylmercury often enters the body through seafood, which is difficult to remove once in the environment or food.
Researchers at the Stanford Synchrotron Radiation Lightsource (SSRL) have identified a surprising key molecule in methylmercury poisoning: S-adenosyl-L-methionine (SAM). This molecule could play a significant role in understanding and addressing the toxicity of methylmercury.
The biological process of mercury methylation was previously unknown, but understanding it is crucial for developing effective strategies to mitigate methylmercury contamination. This study represents an important step toward uncovering that process, which is essential for future remediation efforts.
The new study addresses a key mystery about how methylmercury is produced. While scientists knew that mercury from industrial emissions is converted into methylmercury by microbes in water, which then accumulates in fish and humans, the exact process remained unclear.
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The difficulty lies in studying the protein system responsible for this conversion, which is called HgcAB. This system is present in very small quantities in microbes, making it hard to isolate and study. Also, HgcAB is highly sensitive to oxygen and light, complicating research efforts.
The researchers created a new protocol to yield enough stable HgcAB to investigate how it finally transforms mercury into methylmercury.
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University of Michigan professor Steve Ragsdale said, “We’ve worked with a lot of very difficult proteins, but this one had everything you would not want to have in a protein if you wanted to purify it. It was very complicated.”
Once the team successfully purified enough HgcAB, they transported the samples to SSRL, keeping them cooled with liquid nitrogen and shielded from light. At SSRL, associate scientist Macon Abernathy studied the protein using extended X-ray absorption fine structure spectroscopy. SSRL’s specialized X-ray facilities, designed for biological samples, were crucial in detecting the very weak signals from the ultra-dilute HgcAB protein samples.
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“No one has tried it yet, but perhaps analogs of SAM could be developed that could address methylmercury in the environment,” Ragsdale said.
Journal Reference:
- Kaiyuan Zheng et al., S-adenosyl-L-methionine is the unexpected methyl donor for the methylation of mercury by the membrane-associated HgcAB complex. Proceedings of the National Academy of Sciences, 15 November 2024 DOI: 10.1073/pnas.2408086121