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Threonine (symbol Thr or T) [2] is an amino acid that is used in the biosynthesis of proteins.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.
In addition to the common amino acid L-tyrosine, which is the para isomer (para-tyr, p-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers, namely meta-tyrosine (also known as 3-hydroxyphenylalanine, L-m-tyrosine, and m-tyr) and ortho-tyrosine (o-tyr or 2-hydroxyphenylalanine), that occur in nature.
Threonine proteases use the amino acid threonine as their catalytic nucleophile. Unlike cysteine and serine, threonine is a secondary hydroxyl (i.e. has a methyl group). This methyl group greatly restricts the possible orientations of triad and substrate as the methyl clashes with either the enzyme backbone or histidine base. [2]
Allothreonine is an amino acid with the formula CH 3 CH(OH)CH(NH 2)CO 2 H. It is the diastereomer of the amino acid threonine. Like most other amino acids, allothreonine is a water-soluble colorless solid. Although not one of the proteinogenic amino acids, it has often been the subject for the synthesis of novel proteins using an expanded ...
In general, deamidation can be eliminated by proteolysis at an acidic pH or at a slightly basic pH (4.5 and 8.0, respectively) using the endoprotease, Glu-C. [2] The rates of deamidation depend on multiple factors, including the primary sequences and higher-order structures of the proteins, pH, temperature, and components in the solutions.
Threonine proteases use the secondary alcohol of their N-terminal threonine as a nucleophile to perform catalysis. [1] [2] The threonine must be N-terminal since the terminal amine of the same residue acts as a general base by polarising an ordered water which deprotonates the alcohol to increase its reactivity as a nucleophile.
The addition of the two molecules typically proceeds in a step-wise fashion to the addition product, usually in equilibrium, and with loss of a water molecule (hence the name condensation). [3] The reaction may otherwise involve the functional groups of the molecule, and is a versatile class of reactions that can occur in acidic or basic ...
Since the proteins have acidic and basic regions, they can serve as both proton donors or acceptors in order to maintain a relatively stable intracellular pH. In the case of a phosphate buffer, substantial quantities of weak acid and conjugate weak base (H 2 PO 4 – and HPO 4 2– ) can accept or donate protons accordingly in order to conserve ...