Newswise — Researchers at the University of California, Berkeley, have discovered how cysteine, an amino acid found in many proteins, activates a key regulator of cell growth in yeast.

The discovery, published in the journal *Cell*, could lead to new therapies for treating diseases such as cancer and obesity, which are characterized by abnormal cell growth.

The key regulator of cell growth in yeast is a protein called TOR (Target of Rapamycin). TOR is a kinase, an enzyme that adds phosphate groups to other proteins, which can activate or deactivate them.

TOR is activated by a variety of factors, including nutrients such as glucose and amino acids. Cysteine is one of the amino acids that can activate TOR.

The researchers found that cysteine activates TOR by binding to a specific cysteine-rich domain in the protein. This binding event causes a conformational change in TOR, which allows it to bind to and phosphorylate its downstream targets.

The researchers also found that cysteine activation of TOR is essential for cell growth in yeast. When they deleted the cysteine-rich domain from TOR, cells were unable to grow.

The discovery that cysteine activates TOR could lead to new therapies for treating diseases such as cancer and obesity. In cancer, cells often have high levels of TOR activity, which can drive cell growth and proliferation. By inhibiting TOR activity, it may be possible to slow or stop the growth of cancer cells.

In obesity, high levels of TOR activity can lead to the accumulation of fat cells. By inhibiting TOR activity, it may be possible to reduce the number of fat cells and promote weight loss.

The researchers are currently working on developing inhibitors of TOR that could be used to treat diseases such as cancer and obesity.

The discovery of how cysteine activates TOR is a significant step forward in our understanding of how cell growth is regulated. This knowledge could lead to new therapies for treating diseases that are characterized by abnormal cell growth.