E3 ligase is a type of enzyme that plays a crucial role in the process of ubiquitination, which is essential for protein regulation within cells. It helps attach a small protein called ubiquitin to target proteins, marking them for degradation or altering their function. This process is vital for maintaining cellular homeostasis and regulating various biological processes. There are many different types of E3 ligases, each with specific target proteins. They are classified into three main families: Hect, RING, and RBR ligases. Understanding how E3 ligases work can provide insights into diseases, including cancer, where protein regulation is often disrupted.