Data collection and processing statistics.

Both crystals belong to the orthorhombic space group P21212 with two 2-fold screw axes (a, b) and a 2-fold axis (c), all angles being 90°. X-ray diffraction reflections were observed with a redundancy (multiplicity) in the range of 3.5 to 4.1, which improved the data quality by averaging observations. In both cases, the overall signal-to-noise ratio I/σ was around 8, reaching its limit of around 2 at the maximum resolution of 2.3 Ångström. The redundancy-dependent factor Rmerge, the redundancy-independent factor Rmeas (Rrim), and the precision indicating Rpim were calculated as deviations from averaged reflection intensities (I) according to the given formulas and indicate the data quality. Solvent content refers to the volume of disordered aqueous buffer within the protein crystal lattice.
*alues in parentheses refer to the highest resolution shell.
aThe redundancy dependent merging R-factor: .
bThe redundancy independent R-factor: .
cThe precision indicating merging R-factor: .
dMean (I/sd(I)) from SCALA.