Description
X-ray macromolecular crystallography is a leading method for understanding the three-dimensional structure of proteins and nucleic acids. Despite the development of new research methods, such as Cryo-EM, crystallographic studies remain the most precise and reliable. However, some cases require unique procedures and deep structural analysis. These "difficult cases" are often abandoned after initial failures. However, studying such structures provides a unique opportunity to learn about nature's surprising abilities to create sophisticated molecular systems with various applications. The presented examples include the following crystal structures: (i) A supramolecular complex formed by encapsulating C60 fullerene in a molecular container built from two resorcin[4]arene rims zipped together by peptidic arms hydrogen bonded into a cylindrical β-sheet [1]. (ii) The crystal structure of a DNA-RNA chimeric duplex in complex with Ba2+ ions, exhibiting complicated twinning (a combination of threefold and twofold rotation) and structural pseudosymmetry [2,3]. (iii) The modulated crystal structure of the ANS complex of Hyp-1 protein with 36 protein molecules and 156 ANS ligands (~ 50 000 non-H atoms) in the asymmetric unit of the supercell and commensurate ninefold modulation, manifested in the diffraction pattern by a wave of reflection-intensity modulation [4]. (iv) The potassium-independent L-asparaginase from Phaseolus vulgaris, comprised of eight (ɑβ)2 dimers (~36 000 non-H atoms) with rare P2 symmetry and pseudosymmetric 41-like helical packing, featuring a huge 18-stranded β-sheet of each dimer extended in both directions by similar β-sheets of its neighbors. An infinite helix running throughout the crystal forms a "protein double-helix".
[1] Gilski, M., Drozdzal, P., Kierzek, R. & Jaskolski, M. (2016). Acta Cryst. D72, 211–223.
[2] Luo Z., Dauter Z. & Gilski M. (2017). Acta Cryst. D73, 940–951.
[3] Gilski M. et al. (2020). Acta Cryst. B76, 815-824.
[4] Smietanska, J. et al. (2020). Acta Cryst. D76, 653-667.
