A new modulated crystal structure of the ANS complex of the St John s wort Hyp 1 protein with 36 protein molecules in the asymmetric unit of the supercell

Superstructure modulation, with violation of the strict short range periodic order of consecutive crystal unit cells, is well known in small molecule crystallography but is rarely reported for macromolecular crystals. To date, one modulated macromolecular crystal structure has been successfully determined and refined for a pathogenesis related class 10 protein from Hypericum perforatum Hyp 1 crystallized as a complex with 8 anilinonaphthalene 1 sulfonate ANS [Sliwiak et al. 2015 , Acta Cryst. D71, 829 843]. The commensurate modulation in that case was interpreted in a supercell with sevenfold expansion along c. When crystallized in the additional presence of melatonin, the Hyp 1 ANS complex formed crystals with a different pattern of structure modulation, in which the supercell shows a ninefold expansion of c, manifested in the diffraction pattern by a wave of reflection intensity modulation with crests at l 9n and l 9n 4. Despite complicated tetartohedral twinning, the structure has been successfully determined and refined to 2.3 amp; 8197; resolution using a description in a ninefold expanded supercell, with 36 independent Hyp 1 chains and 156 ANS ligands populating the three internal 95 ligands and five interstitial 61 ligands binding sites. The commensurate superstructures and ligand binding sites of the two crystal structures are compared, with a discussion of the effect of melatonin on the co crystallization proces