Unnatural Amino Acid Recognition by Orthogonal tRNA/Synthetase Pairs

An orthogonal tRNA/synthetase pair recognizes an unnatural amino acid through a process called 'expanded genetic code translation.' This process involves the modification of a natural tRNA and the corresponding aminoacyl-tRNA synthetase to incorporate an unnatural amino acid into the growing polypeptide chain during protein synthesis.

The orthogonal tRNA is engineered to have a unique anticodon sequence that does not naturally occur in the cell. This anticodon sequence is designed to specifically recognize and pair with a corresponding codon sequence in the mRNA that codes for the unnatural amino acid. The orthogonal tRNA is also modified to be compatible with the cell's translation machinery, allowing it to be recognized and utilized during protein synthesis.

On the other hand, the orthogonal aminoacyl-tRNA synthetase is engineered to specifically recognize and aminoacylate the orthogonal tRNA with the unnatural amino acid. This synthetase is designed to have a unique binding pocket that specifically accommodates the unnatural amino acid, ensuring its selective attachment to the tRNA.

Overall, the orthogonal tRNA/synthetase pair works together to recognize and incorporate the unnatural amino acid into the growing polypeptide chain, expanding the genetic code and enabling the incorporation of non-natural amino acids into proteins.