Why high levels of the amino acid cysteine are toxic to cells
Cysteine is one of the main building blocks that cells use to make proteins. But this amino acid is a double-edged sword—too much cysteine is toxic to the cell. Cells therefore keep free cysteine levels to a minimum, converting most of the amino acid into the antioxidant glutathione.
Cysteine is a crucial amino acid for protein synthesis and cellular function, but it can be toxic in high concentrations. A new study published in Nature Metabolism reveals that high levels of cysteine can strip iron from ferritin, a protein complex that stores iron safely. This leads to a surge of free iron in the mitochondria, causing damage to iron-sulfur proteins and ultimately cell death.
Cysteine is indispensable for building iron-sulfur clusters and generating the antioxidant glutathione, but too much of it overwhelms the cell's ability to manage it. Cells naturally keep cysteine levels low by converting it into glutathione, a process that also triggers cell death when cysteine is in excess. Understanding why cells preferentially maintain low levels of cysteine over glutathione provides insight into the evolution of cellular mechanisms and may have implications for disease research, particularly in cancer cell metabolism.
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