Thr

Thr is the three-letter code for the amino acid threonine, one of the 20 standard amino acids used to build proteins. In protein sequences, Thr is used to denote threonine, while the single-letter code is T.

Chemically, threonine is a polar, uncharged amino acid. Its side chain includes a beta-hydroxyl group (-CH(OH)CH3), which makes it a common site for post-translational modification such as phosphorylation. This property contributes to the regulation of enzyme activity and signaling pathways in cells.

Biology and metabolism: In humans, threonine is considered an essential amino acid, meaning it must be obtained from the diet because the body cannot synthesize adequate amounts. In many bacteria and plants, threonine is synthesized via the aspartate family pathway, with key enzymes encoded by genes such as thrA, thrB, and thrC in some organisms forming part of the threonine biosynthetic route.

Genetic coding: Threonine is encoded by four codons in messenger RNA: ACU, ACC, ACA, and ACG. In DNA, these correspond to ACT, ACC, ACA, and ACG respectively. This redundancy helps protect threonine translation against mutations.

Dietary sources and nutrition: Good dietary sources include meat, dairy products, eggs, and certain plant-based foods such as legumes and quinoa. Adequate threonine intake supports protein synthesis, immune function, and overall nitrogen balance.

See also: Threonine, protein structure, amino acid biosynthesis.