Collision-free configuration-spaces in macromolecular crystals

Molecular replacement (MR) is a well-established computational method for phasing in macromolecular crystallography. In MR searches, spaces of motions are explored for determining the appropriate placement of rigid single-body (or articulated multi-rigid-body) models of macromolecules in crystallographic asymmetric units. This paper investigates which portion of the motion space is physically realizable given that packing of protein molecules in a crystal are subject to the constraint that they cannot interpenetrate. This imposes severe restrictions on which points in the motion space are accessible. By determining a priori which portions of motion space correspond to symmetry mates in collision, it becomes feasible to construct more efficient MR techniques which avoid searching in those regions of motion space.