Why does citrullination occur?

Why does citrullination occur?

• A. Part of apoptosis
• B. Part of phagocytosis
• C. Part of mitosis
• D. Part of replication

Answer: (A)

Citrullination is a calcium-dependent post-translational modification in which peptidyl arginine deiminases convert arginine residues in proteins to citrulline. This modification tends to happen when cells are undergoing programmed death, because apoptosis involves a rise in intracellular calcium that activates PAD enzymes. Once activated, PADs citrullinate various proteins, altering their function and properties, which helps in the systematic breakdown and clearance of the dying cell and can also create modified targets that influence immune responses. The other listed cellular processes—phagocytosis, mitosis, and replication—rely on different sets of enzymes and mechanisms (such as cytoskeletal remodeling for engulfment, kinases for chromosome segregation, and DNA synthesis enzymes for replication) and do not center on PAD-mediated citrullination. Thus, citrullination occurs as part of apoptosis in this context.

Citrullination is a calcium-dependent post-translational modification in which peptidyl arginine deiminases convert arginine residues in proteins to citrulline. This modification tends to happen when cells are undergoing programmed death, because apoptosis involves a rise in intracellular calcium that activates PAD enzymes. Once activated, PADs citrullinate various proteins, altering their function and properties, which helps in the systematic breakdown and clearance of the dying cell and can also create modified targets that influence immune responses. The other listed cellular processes—phagocytosis, mitosis, and replication—rely on different sets of enzymes and mechanisms (such as cytoskeletal remodeling for engulfment, kinases for chromosome segregation, and DNA synthesis enzymes for replication) and do not center on PAD-mediated citrullination. Thus, citrullination occurs as part of apoptosis in this context.