Subtle changes in protein composition by a process called ‘citrullination’ are thought to be involved in causing several diseases, including multiple sclerosis. Researchers from Karolinska Institutet now show in the journal Cell Reports that the enzyme PAD2, the main protein responsible for this process in the brain, also plays an important role in the normal development of a subset of brain cells, known as oligodendrocytes, and in their function in stimulating neuronal communication.