Table 1. Data collection, refinement, and stereochemistry statistics.

R_merge=Σ_hkl|I_i(hkl)−〈I(hkl)〉|/Σ_hklI_i(hkl), where I_i(hkl) is the intensity of an observation and 〈I(hkl)〉 the mean value for its unique reflection. Summations cover all reflections.

R_work=Σ_hkl|F_obs−k·F_calc|/Σ_hklF_obs. R_free was as per R_work, but with the reflections excluded from refinement. The R_free set was chosen using default parameters in PHENIX (Adams et al, 2010).

Ramachandran plot categories were defined by MolProbity (Chen et al, 2010).