Module 1: Figure protein ubiquitination
Protein ubiquitination in cell signalling and protein degradation.
Covalent modification of proteins by ubiquitin has two important functions. As shown in the top panel, reversible ubiquitination of protein substrates alters their conformation enabling them to carry out various signalling functions in the control of cellular responses. The bottom panel illustrates how the ubiquitination of certain proteins marks them out for degradation by the proteasome. Before they enter the proteasome, deubiquitinases (DUBs) remove the ubiquitin, which is recycled back to be used again by the ligases. The way in which these ligases function to ubiquitinate proteins is shown in Module 1: Figure ubiquitin–proteasome system.