Data collection, phasing and refinement statistics.

Numbers in parentheses refer to values in the highest resolution shell.aRsym = ΣjΣh|Ih,j−Ih>|/ΣjΣhIh> where Ih,j is the jth observation of reflection h, and Ih> is the mean intensity of that reflection.bRcryst = Σ||Fobs|−|Fcalc||/Σ|Fobs| where Fobs and Fcalc are the observed and calculated structure factor amplitudes, respectively.cRfree is equivalent to Rcryst for a 4% subset of reflections not used in the refinement.