Switching between low and high affinity for the Syk tandem SH2 domain by irradiation of azobenzene containing ITAM peptidomimetics.

Spleen tyrosine kinase (Syk) plays an essential role in IgE receptor signaling (FcepsilonRI), which leads to mast cell degranulation. Divalent binding of the tandem SH2 domain (tSH2) of Syk to the intracellular ITAM motif of FcepsilonRI activates the kinase domain of Syk, and thereby initiates cell degranulation. The inter SH2 domain distance in Syk tSH2 might be important for Syk kinase activation. In this study, photoswitchable ITAM peptidomimetics containing an azobenzene moiety were synthesized. Irradiation of these constructs changes the distance between the two SH2 binding epitopes and therefore, they may be used as photoswitches. The affinity of the cis- and trans-isomer for tSH2 was assayed with SPR. The ITAM peptidomimetic with the smallest linker displayed the largest difference in affinity between the two isomers (at least 100-fold), and the affinity of the cis-isomer was comparable to monovalent binding. The ITAM mimics with larger photoswitchable linkers displayed modest differences. These results indicate that Syk tSH2 is able to adapt the inter SH2 domain distance to ligands larger than native ITAM, but not to smaller ones. 2009 European Peptide Society and John Wiley & Sons, Ltd.