Terminal deoxynucleotidyl transferase

Terminal deoxynucleotidyl transferase (TdT) is an enzyme that belongs to the DNA polymerase family. It is unique among DNA polymerases due to its ability to add nucleotides to the 3' end of a DNA molecule without the need for a DNA template. This process is known as DNA synthesis.

Function

TdT is primarily involved in the process of V(D)J recombination, which is crucial for the development of B cells and T cells in the immune system. During this process, TdT adds random nucleotides to the DNA during the recombination of the Variable (V), Diversity (D), and Joining (J) gene segments. This results in a diverse range of antibodies and T cell receptors, allowing the immune system to respond to a wide array of pathogens.

Structure

TdT is a monomeric protein that contains a catalytic core, which is responsible for the addition of nucleotides. This core is surrounded by a regulatory region that controls the activity of the enzyme. The structure of TdT is similar to other DNA polymerases, but it lacks a proofreading domain, which is why it can add nucleotides without a DNA template.

Clinical significance

Due to its role in the immune system, abnormalities in TdT can lead to various health conditions. For instance, overexpression of TdT is often seen in certain types of leukemia, making it a useful marker for diagnosing this disease. On the other hand, a deficiency in TdT can result in a weakened immune system, leading to increased susceptibility to infections.

See also

• DNA polymerase
• V(D)J recombination
• Immune system
• Leukemia