Fragment screening on chimeric constructs

Crystallographic fragment screening is a valuable tool for screening compounds in the early stages of drug-discovery projects. In this project we aim at performing a crystallographic fragment screening for cargo-specific binders of the TPR domain of the kinesin-1 light chain (KLC1TPR). This approach was inspired by the observation of the serendipitous stabilisation of a mobile loop in the X-ray crystal structure of KLC1TPR in complex with the engineered KinTag peptide ligand. This complex crystallizes with six molecules in the asymmetric unit positioned such that their concave surfaces face each other in pairs with a head-to-tail arrangement. Within each pair, this organization stabilizes in trans an otherwise disordered loop held in place by residues contributed both by the TRP domain and the cargo peptide. This observation suggested that it might be possible to target cargo-specific interactions using small molecules. Crystals of KLC1TPR in complex with either JIP1 or TorsinA ‘Y-acidic’ peptides (KLC1TPR:Y-acidicpept) are ideally suited for this. Both complexes crystallize with their TPR-peptide interface exposed to the solvent thus fully accessible to fragments. When crystallized in presence of a KLC1-specific Nanobody these crystals typically diffract to an acceptable resolution (~2.5 Å).