Discovery of highly potent Src SH2 binders: structure-activity studies and X-ray structures.

Optimization of the hydrophobic moiety of caprolactam/thiazepinone based compounds led to the identification of potent Src SH2 binders in two different series incorporating a phosphotyrosine group (RU 81843) or a phosphobenzoic group (RU 79181). The X-ray co-structures with the Src SH2 domain revealed different binding modes for RU 81843 and RU 79181, and an excellent fit between RU81843 and the Src SH2 protein thus explaining its high potency (9 nM, 15-fold more potent than pYEEI reference peptide).

Imidazole-based ligands of the Src SH2 protein.

Starting from known Src SH2 inhibitors incorporating five-membered heterocycles or benzamide scaffolds, we prepared tetrasubstituted imidazole compounds able to interact with the pY, pY+1 and pY+3 binding sites of the Src SH2 protein. The synthesis and biological data are presented.

The influence of fibrin(ogen) fragments on the kinetic parameters of the tissue-type plasminogen-activator-mediated activation of different forms of plasminogen.

In the present work we have determined Km,app and kcat,app values for tissue-type plasminogen-activator-catalyzed activation of Glu-plasminogen, Lys-plasminogen and mini-plasminogen in the absence and in the presence of fibrinogen-derived fragments. These were CNBr fragment 2, the A alpha chain remnant of CNBr fragment 2 (A alpha 148-207) and plasmin-generated fragment D-EGTA. The time course of plasmin formation from the various types of plasminogen (plg) was measured spectrophotometrically in a coupled assay system where D-valyl-L-leucyl-L-lysine p-nitroanilide served as a plasmin substrate.

Fibrinogen lysine residue A alpha 157 plays a crucial role in the fibrin-induced acceleration of plasminogen activation, catalyzed by tissue-type plasminogen activator.

In previous studies, we have shown that the stretch 148-197 of the fibrinogen A alpha chain plays a crucial role in the acceleration of the tissue-type plasminogen activator (t-PA)-catalyzed plasminogen activation. In this study we have synthesized parts of A alpha 148-197 and analogues thereof. We found that the peptides with sequences identical with A alpha 148-161 and A alpha 149-161 of human fibrinogen accelerate the plasminogen activation by t-PA, whereas the corresponding peptides in which lysine residues A alpha 157 had been replaced by valine or arginine had no accelerating capacity.

Identification of a site in fibrin(ogen) which is involved in the acceleration of plasminogen activation by tissue-type plasminogen activator.

The rate of activation of plasminogen by tissue-type plasminogen activator is greatly increased by fibrin, but not by fibrinogen. A possible explanation for this phenomenon could be that conformational changes take place during the transformation of fibrinogen to fibrin which lead to exposure of sites involved in the accelerated plasmin formation. This is also supported by our recent observation that some enzymatically prepared fragments of fibrinogen and fibrin (D EGTA, D-dimer, Y) and also CNBr fragment 2 from fibrinogen have this property.