The Definitive Hitchhiker's Guide to Pathological Macromolecular Crystals Editorial for Crystallography Reviews, Issue 1 of 2020

As the authors say, they give a ‘The Definitive Hitchhiker’s Guide to Pathological Macromolecular Crystals’ in their tutorial review article ‘Characterizing pathological imperfections in macromolecular crystals: lattice disorders and modulations’ by Jeffrey J. Lovelace andGloria E.O. Borgstahl fromTheEppley Institute forResearch inCancer andAlliedDiseases,University ofNebraskaMedical Center,Omaha,USA. Fourmain categories of pathological crystals are described from the easiest to themost difficult: rotational order/disorder (ROD), layer translocation defect (LTD), translational non-crystallographic symmetry (tNCS) and modulation. The paper provides an easy to follow experimental pathway to solve each malady, the descriptions of crystal issues are given, the symptoms and ways of solution are detailed. The review article ‘Introduction to crystallographic refinement of macromolecular atomic models’ by Alexandre G. Urzhumtsev from the IGBMC, CNRS-INSERM Illkirch andUniversité de Lorraine, Nancy, France andVladimir Y. Lunin fromKeldysh Institute of Applied Mathematics of Russian Academy of Sciences, Moscow, Russia [1] is now accomplished with an addendum by the authors. The review section ‘5.8.2 Subatomic resolution’ is completedwith some historical details, especially with a reference of a forgotten article by Rosalind Franklin in Nature [2]. Franklin showed in 1950 the impact of bond electrons on structure factors, moreover she modelled their contribution as that from point scatterers at the middle of bonds. This was the first attempt on modelling of deformation density. A Statement by Dietmar Stalke, Regine Herbst-Irmer and their co-workers from the Institute for Inorganic Chemistry, University Göttingen, Germany is issued on the review ‘Metrics for crystallographic diffractionand fit-data: a reviewof existing ones and the need for new ones’ from Julian Henn [3] as he refers two of their examples as case studies. The overall aim is to improve X-ray structure analyses, addressing issues with σ (Io)s, as well as to avoid overfitting in charge densitymodels. The community of Crystallographers is aware of the need for improvement in hardware and software and the upcoming developments towards data quality need to be discussed. The book ‘Data analytics for protein crystallization’ edited by Marc L. Pusey and Ramazan SavaşAygűn in 2017 is part of theComputational Biology series of Springer International Publishing AG. It was reviewed by Ivana Kuta Smatanova from the University of South Bohemia, Czech Republik. Successful crystallization of biological macromolecules depends on the purification process and the crystallization methodology; on the balance of the large number of variables in solution composition and final purity of the protein are critical. The book provides a mathematical-physical interpretation of crystallization, with an improved theoretical insight into the processes of nucleation and crystal growth.