Tyrosine—tRNA ligase

Tyrosine—tRNA ligase, also known as tyrosyl-tRNA synthetase, is an enzyme that belongs to the class of aminoacyl-tRNA synthetases (aaRS). This enzyme plays a crucial role in the process of protein synthesis by attaching the amino acid tyrosine to its corresponding transfer RNA (tRNA^Tyr), a step critical for the translation of messenger RNA (mRNA) into protein. The enzyme is encoded by the YARS gene in humans.

Function

Tyrosine—tRNA ligase catalyzes a two-step reaction. In the first step, tyrosine is activated by ATP to form tyrosyl-AMP, a high-energy intermediate. In the second step, the activated tyrosine is transferred to the 3' end of tRNA^Tyr. This reaction is crucial for the genetic code to be translated into a sequence of amino acids, leading to protein synthesis. The specificity of this enzyme ensures that only tyrosine is attached to tRNA^Tyr, which is essential for maintaining the accuracy of protein synthesis.

Structure

The structure of tyrosine—tRNA ligase varies among different species, but it generally consists of two main domains: the catalytic domain, which is responsible for the activation of tyrosine and the transfer to tRNA, and the anticodon-binding domain, which recognizes the tRNA^Tyr. The enzyme can exist in both monomeric and dimeric forms, depending on the organism and cellular conditions.

Clinical Significance

Mutations in the YARS gene, which encodes the tyrosine—tRNA ligase, have been associated with various human diseases. These include Charcot-Marie-Tooth disease, a disorder affecting the peripheral nerves, and a predisposition to autoimmune diseases due to the enzyme's role in immune response regulation. Understanding the function and structure of tyrosine—tRNA ligase is therefore important not only for basic biological research but also for clinical applications.

Evolution

Tyrosine—tRNA ligase is part of the aminoacyl-tRNA synthetase family, which is believed to be among the first proteins to have evolved. This is due to their central role in protein synthesis, making them essential for the survival of all living organisms. The evolutionary conservation of these enzymes, including tyrosine—tRNA ligase, underscores their fundamental importance in biology.

See Also

• Aminoacyl-tRNA synthetase
• Protein synthesis
• Genetic code
• Charcot-Marie-Tooth disease