When fragment screening is carried out using X-ray crystallography it reveals the 3D-position of the fragment hits inside the protein’s binding site. This additional information of the fragment’s position is highly valuable for further improvement of the usual “low-affinity fragments” to create binders of higher potency. By combining fragment-based and structure-based drug discovery, binders of higher potency can be achieved.
At the macromolecular crystallography (MX) beamlines at BESSY II, a dedicated workflow was established for the user community. It fosters efficient and convenient screening and is based on several unique developments: First, the very diverse F2X fragment libraries that deliver high hit rates, mostly in the range of 20-25%.[2,3] Second, tools like the EasyAccess Frame ensure fast and comfortable crystal soaking and harvesting. After data collection at the state-of-the-art MX beamlines at BESSY II, data analysis is highly automated and conveniently interfaced via the FragMAXapp setup at HZB. FragMAXapp enables automatic data treatment using a number of pipelines, including the HZB-developments XDSAPP for automatic processing and fspipeline for automatic refinement.[6,7] As a final step, improved methodologies like PanDDA are applied for the best identification of the fragments in the electron density.
Beyond efficient MX-based screening, HZB also offers methods of hit evolution to higher potency via fragment growing. In HZB’s Frag4Lead workflow the 3D-information of the crystallographic hits are used as an anchor for virtual pre-screening of suitable candidates from chemical catalogs. This way, the first fragment growing step can be achieved without the need for custom synthesis and minimal virtual-screening expertise. Jan and team successfully employed Frag4Lead to advance fragment hits to single-digit micromolar binders in one step and shall report about this.
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