Significant compensatory role of position Y-2 conferring high affinity to non-phosphorylated inhibitors of Grb2-SH2 domain

Systematic modification of amino acid at position Y-2 of a library-derived non-phosporylated thioether-cyclized peptide, cyclo(CH2CO-Glu−2-Leu-Tyr0-Glu-Asn-Val-Gly-Met-Tyr-Cys)-amide, aided by molecular modeling, demonstrates that the Glu−2 sidechain compensates for the absence of Tyr0 phosphorylation in retaining effective binding to Grb2-SH2 domain. Replacement of Glu−2 with γ-carboxy-glutamic acid produced a high affinity inhibitor, the first example with submicromolar affinity (IC50 = 640 nM).