Side-chains threonine

As mentioned above, in the case of glutamine or asparagine residues the side-chain amide groups have to be protected or alternatively, preformed and purified active esters have to be used. When unprotected side-chain threonine derivatives are activated, a partial (3-elimination to a-aminocrotonic acid has been reported,f l whereas arginine, either unprotected and protonated or as co-tosyl derivative may cyclize to a 6-lactam during activa-tion.f l... 

Figure 4.4 Schematic diagram of the structure of the a/p-barrel domain of the enzyme methylmalonyl-coenzyme A mutase. Alpha helices are red, and p strands are blue. The inside of the barrel is lined by small hydrophilic side chains (serine and threonine) from the p strands, which creates a hole in the middle where one of the substrate molecules, coenzyme A (green), binds along the axis of the barrel from one end to the other. (Adapted from a computer-generated diagram provided by P. Evans.)...

In both structures the ion is coordinated to six ligands with octahedral geometry. Four water molecules as well as the side chain oxygen atom of a serine residue from the P-loop and one oxygen atom from the (3-phosphate bind to Mg + in the GDP structure. Two of the water molecules are replaced in the GTP structure by a threonine residue from switch I and an oxygen atom from the y phosphate (similar to the arrangement shown in... 

A variety of cellular and viral proteins contain fatty acids covalently bound via ester linkages to the side chains of cysteine and sometimes to serine or threonine residues within a polypeptide chain (Figure 9.18). This type of fatty acyl chain linkage has a broader fatty acid specificity than A myristoylation. Myristate, palmitate, stearate, and oleate can all be esterified in this way, with the Cjg and Cjg chain lengths being most commonly found. Proteins anchored to membranes via fatty acyl thioesters include G-protein-coupled receptors, the surface glycoproteins of several viruses, and the transferrin receptor protein. 

Copolymers of a-hydroxy acids and a-amino acids are one type of poly(ester-amide)s and are called polydepsipeptides (PDPs) [17]. Since some of natural occurring a-amino acids, typically Asp, Glu, lysine (Lys), cysteine (Cys), serine (Ser), and threonine (Thr), possess reactive (hydrophilic) side-chain groups, PDPs... 

Succinic anhydride also may react with protein phenolate side chains of tyrosine residues and the —OH group of aliphatic hydroxy amino acids (Figure 1.82). The phenolate ester derivatives are unstable above pH 5.0, whereas the serine and threonine esters are more stable but may be cleaved by treatment with hydroxylamine at basic pH (Gounaris and Perlman, 1967). 

Similarly to 17 Th neutral loss, 18Th mass shifts are also very common, corresponding to the loss of water. Such shifts are (in most cases) caused by elimination of hydroxyl group from serine and threonine side chains. 

Small side chains (SSC) =glycine+alanine+serine, Polar chains (PC) =aspartic acid+threonine+serine+glutamic acid+tyrosine+lysine +histidine+arginine. 

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