Phosphoserine/threonine

Following the style of presentation used in Imperiali s paper concerning the synthesis of caged phosphopeptides the general route for synthesis of peptides containing 2-nitrophenylethyl-caged phosphoserine-threonine and tyrosine residue is presented below. 

Yaffe, M. B., and Elia, A. E. (2001). Phosphoserine/threonine-binding domains, Curr Opin Cell Biol 13,131-8. 

Yaffe, M.D. Elia, A.E.H. (2001) Phosphoserine/threonine-binding domains. Curr. Opin. Cell Biol. 13, 131-138. 

Phosphotyrosine phosphatases are only one of several classes of phosphatases. It has been estimated that about a thousand phosphatases of different specificities exist. Here, we consider only cytosolic and receptor tyrosine phosphatases (Fig. 3.8) (phosphoserine/threonine phosphatases are discussed in Chapter 7). 

PP2 C) coordinated by Asp, Asn, and His residnes to form a bin-nclear metal center in the active site. This metal center is bridged by a well-ordered water molecnle. In the proposed hydrolysis mechanism, the metal-bonnd water acts as the nncleophUe to attack the phosphorons center of phosphoserine/threonine. The metal centers contribnte by Lewis acid catalysis to lower the pKa of the bonnd water and to enhance its nncleophiUcity. 

Phosphorylation of proteins on Ser/Thr residues is one of the most common regulatory modifications of signaling proteins (see Chapters 2 and 7). Only recently has it been recognized that serine/threonine phosphorylation results in the formation of multiprotein signaling complexes through specific interactions between phosphory-lated sequence motifs and the following phosphoserine/threonine-binding domains (review Yaffe and Elia, 2001). 

As described earlier, the ability to site specifically replace one amino acid with another genetically encoded residue provides extraordinary access to analyze protein structure and function. An area where it is often applied is in the assessment of the role of phosphorylation of side chains. Typically, two classes of mutants are made those that prevent modification (nonphosphorylatable) and those that are constitutive (nonhydrolyzable) phosphorylated mimics. For the former, the phosphorylatable residues Ser and Thr are replaced with Ala, and Tyr with Phe (Fig. 7.2-3). These are reasonably successful in many cases, although they can be misleading because they lack the hydrogen-bonding and polarity characteristics of the authentic residues [19]. More difficult is the substitution of a phosphoamino acid with one of the 20 encoded residues. Phosphoserine/threonine is commonly replaced with Asp or Glu residues (Fig. 7.2-4). However, Asp and Glu are deficient in several respects. First,... 

Asp and Glu are considerably smaller than phosphoserine/threonine. Second,... 

P White, J Beythien. Preparation of phosphoserine, threonine and tyrosine containing peptides by the Fmoc methodology using pre-formed phospho-amino acid building blocks. Proceedings of Innovation and Perspectives in Solid Phase Synthesis. Fourth International Symposium, Edinburgh, 1995, pp 557-560. 

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