A new default restraint library for the protein backbone inPhenix Phenix: a conformation-dependent geometry goes mainstream

Chemical restraints are a fundamental part of crystallographic protein structure refinement. In response to mounting evidence that conventional restraints have shortcomings, it has previously been documented that using backbone restraints that depend on the protein backbone conformation helps to address these shortcomings and improves the performance of refinements [Moriartyet al. et al. (2014),FEBS J. FEBS J.281 281, 4061-4071]. It is important that these improvements be made available to all in the protein crystallography community. Toward this end, a change in the default geometry library used byPhenix Phenix is described here. Tests are presented showing that this change will not generate increased numbers of outliers during validation, or deposition in the Protein Data Bank, during the transition period in which some validation tools still use the conventional restraint libraries.