Protein methylation is a biochemical process where a methyl group (CH₃) is added to specific amino acids in a protein. This modification can occur on lysine or arginine residues and plays a crucial role in regulating protein function, stability, and interactions. Methylation can influence various cellular processes, including gene expression and signal transduction. The enzymes responsible for adding methyl groups are called methyltransferases, while those that remove them are known as demethylases. Dysregulation of protein methylation has been linked to several diseases, including cancer and neurodegenerative disorders, highlighting its importance in maintaining cellular health and function.