Posttranslational modification of proteins

• Some proteins contain amino acids other than the standard 20. These modified amino acids
• include hydroxyproline, methylhistidine, and phosphoserine. However, each of these amino acids
• is clearly derived from one of the standard 20 amino acids. These amino acids are made by
• posttranslational modification of the protein after it has been released from the ribosome; you
• will learn more about posttranslational modification of proteins