Crystallographic data collection and refinement statistics.

aRmerge = (Σ|I−|)/ΣI, where I is the observed intensity and is the average intensity. bRfactor = Σ∥Fo|−|Fc∥/Σ|Fo|. Rfree is calculated with the same equation, but with 5% of reflections not used in the refinement. cRamachandran statistics are given as the number of amino acids that lie within each region, and the percentage is given in parenthesis. Values in parenthesis are for the outermost resolution shell (3.15 Å – 3.1 Å).