Threonine (symbol ThrorT)[2] is an amino acid that is used in the biosynthesisofproteins. It contains an α-amino group (which is in the protonated −NH+ 3 form when dissolved in water), a carboxyl group (which is in the deprotonated −COO− form when dissolved in water), and a side chain containing a hydroxyl group, making it a polar, uncharged amino acid. It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet. Threonine is synthesized from aspartate in bacteria such as E. coli.[3] It is encoded by all the codons starting AC (ACU, ACC, ACA, and ACG).
Threonine sidechains are often hydrogen bonded; the most common small motifs formed are based on interactions with serine: ST turns, ST motifs (often at the beginning of alpha helices) and ST staples (usually at the middle of alpha helices).
The threonine residue is susceptible to numerous posttranslational modifications. The hydroxylside-chain can undergo O-linked glycosylation. In addition, threonine residues undergo phosphorylation through the action of a threonine kinase. In its phosphorylated form, it can be referred to as phosphothreonine. Phosphothreonine has three potential coordination sites (carboxyl, amine and phosphate group) and determination of the mode of coordination between phosphorylated ligands and metal ions occurring in an organism is important to explain the function of the phosphothreonine in biological processes.[4]
Threonine is one of two proteinogenic amino acids with two stereogenic centers, the other being isoleucine. Threonine can exist in four possible stereoisomers with the following configurations: (2S,3R), (2R,3S), (2S,3S) and (2R,3R). However, the name L-threonine is used for one single stereoisomer, (2S,3R)-2-amino-3-hydroxybutanoic acid. The stereoisomer (2S,3S), which is rarely present in nature, is called L-allothreonine.[7]
As an essential amino acid, threonine is not synthesized in humans, and needs to be present in proteins in the diet. Adult humans require about 20 mg/kg body weight/day.[8] In plants and microorganisms, threonine is synthesized from aspartic acid via α-aspartyl-semialdehyde and homoserine. Homoserine undergoes O-phosphorylation; this phosphate ester undergoes hydrolysis concomitant with relocation of the OH group.[9] Enzymes involved in a typical biosynthesis of threonine include:
In humans the gene for threonine dehydrogenase is an inactive pseudogene,[10] so threonine is converted to α-ketobutyrate. The mechanism of the first step is analogous to that catalyzed by serine dehydratase, and the serine and threonine dehydratase reactions are probably catalyzed by the same enzyme.[11]
Research of Threonine as a Dietary Supplement in Animals[edit]
Effects of threonine dietary supplementation have been researched in broilers.[17]
An essential amino acid, threonine is involved in the metabolism of fats, the creation of proteins, the proliferation and differentiation of embryonic stem cells, and the health and function of the intestines. Animal health and illness are strongly correlated with the need for and metabolism of threonine. Intestinal inflammation and energy metabolism disorders in animals may be alleviated by appropriate amounts of dietary threonine. Nevertheless, because these effects pertain to the control of nutrition metabolism, more research is required to confirm the results in various animal models. Furthermore, more research is needed to understand how threonine controls the dynamic equilibrium of the intestinal barrier function, immunological response and gut flora.[18]
^Jastrzab, Renata (2013). "Studies of new phosphothreonine complexes formed in binary and ternary systems including biogenic amines and copper(II)". Journal of Coordination Chemistry. 66 (1): 98–113. doi:10.1080/00958972.2012.746678
^ abManoli, Irini; Sloan, Jennifer L.; Venditti, Charles P. (1993), Adam, Margaret P.; Feldman, Jerry; Mirzaa, Ghayda M.; Pagon, Roberta A. (eds.), "Isolated Methylmalonic Acidemia", GeneReviews®, Seattle (WA): University of Washington, Seattle, PMID20301409, retrieved 2024-03-09
^Shchelochkov, Oleg A.; Carrillo, Nuria; Venditti, Charles (1993), Adam, Margaret P.; Feldman, Jerry; Mirzaa, Ghayda M.; Pagon, Roberta A. (eds.), "Propionic Acidemia", GeneReviews®, Seattle (WA): University of Washington, Seattle, PMID22593918, retrieved 2024-03-09
Y
