Bimolecular fluorescence complementation demonstrates that the c-Fes protein-tyrosine kinase forms constitutive oligomers in living cells

Small-molecule inhibitors of the c-Fes protein-tyrosine kinase

The c-Fes protein-tyrosine kinase modulates cellular signaling pathways governing differentiation, the innate immune response, and vasculogenesis. Here, we report the identification of types I and II kinase inhibitors with potent activity against c-Fes both in vitro and in cell-based assays. One of the most potent inhibitors is the previously described anaplastic lymphoma kinase inhibitor TAE684. The crystal structure of TAE684 in complex with the c-Fes SH2-kinase domain showed excellent shape complementarity with the ATP-binding pocket and a key role for the gatekeeper methionine in the inhibitory mechanism. TAE684 and two pyrazolopyrimidines with nanomolar potency against c-Fes in vitro were used to establish a role for this kinase in osteoclastogenesis, illustrating the value of these inhibitors as tool compounds to probe the diverse biological functions associated with this unique kinase.

Fluorescence response profiling for small molecule sensors utilizing the green fluorescent protein chromophore and its derivatives

Using a fluorescence response profile, a systematic examination was performed for synthetic chromophores of the green fluorescent protein (GFP) to discover new small molecule sensors. A group of 41 benzylideneimidazolinone compounds (BDI) was prepared and screened toward 94 biologically relevant analytes to generate fluorescence response profiles. From the response pattern, compounds containing aminobenzyl and heteroaromatic cyclic substructures revealed a pH dependent emission decrease effect, and unlike other fluorescence scaffolds, most BDIs showed fluorescence quenching when mixed with proteins. On the basis of the primary response profile, we obtained three selective fluorescence turn-on sensors for pH, human serum albumin (HSA), and total ribonucleic acid (RNA). Following analysis, a fluorescence response profile testing four nucleic acids revealed the alkyloxy (Ph-OR) functional group in the para position of benzyl analogues contributes to RNA selectivity. Among the primary hit compounds, BDI 2 showed outstanding selectivity toward total RNA with 5-fold emission enhancement. Finally, BDI 24 showed selective fluorescence increase to HSA (K(d) = 3.57 μM) with a blue-shifted emission max wavelength (Δλ(em) = 15 nm). These examples of fluorescence sensor discovery by large-scale fluorescence response profiling demonstrate the general applicability of this approach and the usefulness of the response profiles.