Table 2. Crystallographic techniques that acquire or model dynamic structural information.

Technique	Information	Drawbacks
Atomic displacement parameters	Thermal vibration	Little relevance to function (Lu et al., 2005 ▶)
Alternative conformations	Coexisting conformations	Static
Ensemble refinement (Gros et al., 1990 ▶; Levin et al., 2007 ▶)	Conformational polymorphism (Lang et al., 2010 ▶)	More parameters and data limitation (Terwilliger et al., 2007 ▶)
Structural comparison	Structural differences	Stable structures only
Chemical trapping	Intermediate, especially after rate-limiting step†	Difficulty in design
Cryotrapping	Intermediate structure	May alter reaction pathway
Time-resolved crystallography	Intermediate and reaction mechanism	Difficulty in rapid reaction initiation

^†To capture an intermediate after a natural rate-limiting step that cannot accumulate to a sufficient concentration, chemical trapping is the only approach possible to slow down or to stall the next step so that the original step is no longer rate-limiting.