(b).

Refinement.

	Uncorrected data	Corrected data‡
Molecules in ASU	2 + 2 monomers	2 monomers
Refined residues	1540	770
Refined waters	1508	754
Rcryst§	0.193	0.180
Rfree¶	0.231	0.210
Average B values (Å2)
Protein	12.3	16.6
Waters	28.8	32.0
Ramachandran plot (%)
Most favored	84.2	84.3
Additionally allowed	15.1	15.1
Generously allowed	0.8	0.6
Disallowed	0.0	0.0
R.m.s.d. bond lengths (Å)	0.012	0.013
R.m.s.d. bond angles (°)	1.3	1.4

^† R _merge = , where 〈I(hkl)〉 is the average intensity of i symmetry-related observations of reflections with Miller indices hkl.

^‡The refinement statistics for corrected data (PDB code 3beq; Xu et al., manuscript in preparation) are shown here for comparison.

^§ R _cryst = , where F _o and F _c are the observed and calculated structure factors.

^¶ R _free was calculated as for R _cryst, but on 5% of data that were excluded prior to refinement.