Macromolecular structures: Quality assessment and biological interpretation

Structure determination using X-ray crystallography involves collection of diffraction data, determination of initial phases followed by iterative rounds of model building and crystallographic refinement to improve the phases and minimize the differences between calculated and observed structure factors. At each of these stages, a variety of statistical filters exist to ensure appropriate validation. Biologically important observations often come from interpretations of signals that need to be carefully deciphered from noise, and therefore human intervention is as important as the automated methods and filters. Currently, all structural data are deposited in the Protein Data Bank (PDB), and this repository is continuously evolving to incorporate new developments in macromolecular crystallography. The journals that publish data arising from structural studies modulate their policies to take cognizance of new improved methodologies. Together, the PDB and journals have evolved an accepted protocol to ensure the integrity of crystallographic results. As a result, the quality of available data and associated interpretations have improved over the years. Typically, if there are differences regarding the mechanism of action of a protein revealed by crystallography then new experiments are carried out to provide further evidence for or against a particular hypothesis. Hence, the scientific systems in structural biology are robust and to a large extent capable of correcting any errors in interpretation of structural results. However, this process is hindered by spurious challenges to published research, based on misuse of validation mechanisms. Such activities are counterproductive and will cause damage to the field of structural biology. © 2017 IUBMB Life, 69(8):563-571, 2017.