Atg4A also known as APG4A is a crucial cysteine protease consisting of 398 amino acids that plays a vital role in autophagy, essential for cellular homeostasis and degradation of damaged organelles and proteins. Located primarily in the cytoplasm, Atg4A is a protein responsible for cleaving the C-terminal part of specific proteins, including GABARAP and MAP1LC3, facilitating autophagosome formation - double-membrane vesicles that engulf cellular debris for lysosomal degradation. Proper functioning of Atg4A regulates autophagy and influences cellular responses to stress and nutrient deprivation. Multiple alternatively spliced isoforms of Atg4A exist, and N-ethylmaleimide can inhibit Atg4A activity, highlighting post-translational modifications in regulatory mechanisms.