ABSTRACT

Protein tyrosine kinases (PTKs), when activated, catalyze the phosphorylation on specific tyrosyl residues of proteins, including PTK themselves. This reaction enables the PTKs to control various cell functions like signal transduction, differentiation and proliferation. An over-activation or mutation of protooncogene encoding protein tyrosine kinases can result in cell transformation(s). Therefore the identification and the synthesis of suitable short and proteolytic resistant PTK peptide substrates or inhibitors can be particularly useful for either the detection of specific enzyme activities or as potential anticancer therapeutics. To this aim, peptides derived from the autophosphorylation site of different PTKs and containing different structural requirements for enzyme recognition have been synthesized and used as substrate of non-receptor tyrosine kinases belonging to the Src and Syk/ZAP70 families.

In contrast to the well-defined consensus sequences specifically recognized by the Ser/Thr protein kinases, the definition of PTK specificity determinants is not clear-cut. This indicates that not only the aminoacid sequence, but also the protein secondary structure is implicated in the substrate recognition by PTKs.

To shed light on this matter we introduced local or global conformational constraints to reduce the possible conformations and obtain information about the different PTK structural requirements to design selective substrates or inhibitors. The inhibitory effect of these derivatives has been tested on non-receptor tyrosine kinases Lyn, Fgr and CSK. A series of potential inhibitors has been also synthesized, derived from PEGY(P)EEVLE, a phosphopeptide which specifically binds to the Src SH2 domain. The effect of this SH2 domain-directed inhibitors has been tested on the Src-like PTK, Fgr.