1.989 and showed clear density for 2 H-atoms (Figure ). Similarly, preliminary solutions obtained from biotin crystals showed 16 atoms and could be further refined structures with an average R 1 /R wall of 0.2873/0.3244 and average GooF of 1.590; these also showed clear density for 2 H-atoms (Figure ). Datasets that could not be stably refined using SHELXLE had R 1 statistics well exceeding 50 % and were not included in subsequent analyses (Figure ). Data from thiostrepton crystals failed to reach atomic resolution but were sufficient for molecular replacement (Figure , Table ). Solutions could be achieved using MOLREP for datasets acquired from thiostrepton under all three fluence conditions, but subsequent refinement was most successful for crystals exposed to the highest fluence of 3.33 e -/Å 2 . Structures determined under these conditions could be refined to R work /R free of 0.2433/0.2488, had an overall B-factor of 11.04 Å 2 , and showed fully intact side chain density for 6 residues, including all five thiazole rings on the molecule. Data collected at the lowest fluence (0.5 e -/Å 2 ) was not generally suitable for high-quality refinement but was still sufficient to visualize the most ordered core of the molecule. In these refinements, side chain density was visible in Fourier difference maps resulting from the refinement of the data against poly-alanine models of thiostrepton (Figure , Supplementary Table ).