Dealing with Aperiodic Protein Crystal Structures - Gloria Borghasti

Protein crystals can be aperiodic. They will diffract X-rays, and are therefore a crystal, but their diffraction is not periodic. This means that their diffraction pattern cannot be simply be indexed by a typical three-dimensional unit cell and space group. Aperiodic crystals include "quasi-
crystals" as well as "modulated" crystals. In the latter case, the modulation can be positional or occupational and these modulations can be incommensurate with the normal periodic lattice [1,6,7]. An overview of aperiodic protein crystal diffraction will be presented with examples. The
discussion will then focus on the characteristics of incommensurately modulated crystals followed by a more detailed discussion of how to solve these crystals. The following details of structure solution will be presented: (1) data collection perils; (2) specialized diffraction data processing in (3+1)D space using a q-vector [2]; (3) how to get an approximation of the
structure in 3D space; (4) the assignment of the (3+1)D space group [4]; and the ultimate (5) crystallographic refinement in superspace[3,5].
References:
[1] Lovelace, Murphy, Narayan, Schutt, Lindberg, Svensson, Wynn, Borgstahl "Protein crystals can be incommensurately modulated" J Appl Cryst 41 , 600-605 (2008).
[2] Porta, Lovelace, Schreurs, Kroon-Batenburg, Borgstahl "Processing incommensurately modulated protein diffraction data with EVAL15", Acta Cryst D67, 628-638 (2011).
[3] Lovelace, Simone, Petricek, Borgstahl, "Simulation of modulated protein crystal structure and diffraction data in a supercell and in superspace" Acta Cryst D69, 1062-1072 (2013).
[4] Porta, J., Lovelace, J., Borgstahl, G. E. O., "How to Assign a (3+1)D Superspace Group to an Incommensurately Modulated Biological Macromolecular Crystal" J. Appl. Cryst. 50, 1200-1207 (2017).
[5] Lovelace J.J., Petricek V., Murshudov G., and Borgstahl G.E.O. “Supercell refinement: a cautionary tale” Acta Cryst. (2019) D75, 852-860.
[6] Lovelace J.J. and Borgstahl G.E.O., “Characterizing pathological imperfections in macromolecular crystals: lattice disorders and modulations” Crystallography Reviews (2020) 26, 3-50.
[7] Lovelace, J. J., and Borgstahl, G. E. O. “Are the St John’s wort Hyp-1 superstructures different?” Acta Cryst. (2021) D77, 790-798.

[@jeffreyohren6624]

When you have a chance, would you please correct Dr. Borgstahl’s name in the title.