Table 1

Crystallographic data, phasing, and refinement. Diffraction data were collected at 100 K on beamline 5.0.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory. A Q4 charge-coupled device detector was used. The selenium atom positions were determined with the peak anomalous difference data in the program Shake-and-Bake v.2.0 (34). MAD phases were generated with MLPHARE (34) and solvent flattening was applied in DM (34). There were eight protein molecules in each asymmetric unit. All selenium atoms except for the NH2-terminal selenomethionines were located, for a total of 48 sites. The model was built with the program O (34). CNS was used for refinement (25, 34). The MLHL maximum likelihood target function was used with density-modified phases as prior experimental phase information. Restrained individualB-factor refinement, anistropic B-factor correction, and a bulk solvent model were used in the refinement. The Protein Data Bank accession code for this protein is 1b4f.

Crystallographic data
Data setλ (Å)dMIN (Å)Observed reflectionsUnique reflectionsCompleteness (%)I〉/〈σiRsym*(%)〈PP〉 acen/cen
Anomalous peak0.979661.95223,26939,54796.517.64.7 (16.3)1.64/0.00
Inflection point0.979821.95168,46938,99795.117.24.2 (18.4)1.24/0.00
High-energy remote0.968591.95183,66039,50796.417.44.8 (24.9)1.73/1.24
Low-energy remote1.000002.00178,02136,23295.219.34.2 (19.5)1.45/1.05
Phasing and refinement
Overall figure of merit to 1.95 ÅMLPHARE: 0.656DM: 0.749
RfactorRcryst: 22.8%Rfree: 27.3%
RMSD from ideality§ Bond lengths: 0.028ÅBond angles: 1.90°
Ramachandran analysisMost favored: 92.5%Additionally allowed: 7.5%
  • * Rsym = ΣhΣi|Ii (h) − 〈/(h)〉|/ΣhI(h)〉, where Ii(h) is theith measurement and 〈I(h)〉 is the weighted mean of all measurements of I(h) for Miller indices h. Values in parentheses are for the highest resolution bins.

  • Phasing power is the mean value of the heavy atom structure factor amplitude divided by the residual lack of closure error for both acentric and centric reflections.

  • R factor = Σ|FoFc|/Σ|Fo|, whereFo and Fc are the observed and calculated structure factors, respectively.Rfree is the cross-validation Rfactor calculated for 10% of the reflections omitted in the refinement process.

  • § RMSD is the root mean square deviation.