A protein inhibitor is a type of molecule that can bind to a specific protein and reduce its activity. These inhibitors can be naturally occurring or synthetically created and are often used in research and medicine to study protein functions or to treat diseases. For example, some cancer therapies use protein inhibitors to block the action of proteins that promote tumor growth. Inhibitors can target various proteins, including enzymes and receptors, and can affect processes like cell signaling and metabolism. By interfering with these proteins, inhibitors can help regulate biological pathways and potentially lead to new treatments for conditions such as diabetes and autoimmune diseases.