Table 1

Data collection, structure determination, and refinement. Diffraction data for chimeric and derivative crystals were collected on a MacScience imaging plate detector DIP2020K (MacScience Corp.) with double focusing Pt/Ni coated mirrors and CuKα x-rays. All other data sets were collected at the Stanford Synchrotron Radiation Laboratory, beamline 7-1 (λ = 1.08 Å) on a MAR imaging plate system. Crystals were stabilized by soaking in synthetic mothor liquor containing 20% ethylene glycol, and subsequently frozen in a 100 K nitrogen gas stream. Data sets were processed with DENZO (25) and scaled with SCALEPACK (25). The structure was solved by MIRAS; heavy atom sites were located with difference Patterson and difference Fourier maps. Sites were refined and initial phases were calculated with ML-PHARE (26), giving a figure of merit of 0.39. This initial phase set was improved and the phases extended to 2.8 Å by solvent flattening and histogram matching with the program DM (27), assuming a solvent content of 65%. All models were constructed with program O (28) and refined with XPLOR (29).

Data collection statistics
Crystal Resolution (Å) Reflections measured (N) Data completeness (%)Rsym(%)〈I/σ〉Sites (N) Phasing powerAnomalous phasing power
AllOuter shellAllOuter shellAllOuter shell
CH32.8 121,53397.798.511.046.374
K2PtCl4 3.0  60,10956.260.5 8.041.29250.880.25
CH3HgCl3.5  43,16689.088.010.341.67231.100.27
Lu (acetate)3 3.5  18,49358.359.015.443.95210.71
TEAS2.25272,50995.296.7 6.327.5116
FHP2.8 136,07298.396.318.753.152
F3-FPP2.15268,07691.570.37.646.983
Refinement statistics
StructureResolution range (Å)Rfactor§ (all data, %)Rfree§ (all data, %)Bond lengths (rmsd,°)Bond angles (rmsd,°)
TEAS 20–2.2519.924.20.0051.21
FHP100–2.8 23.428.10.0111.29
F3-FPP 40–2.2525.029.40.0191.42
  • * Figure of merit = ∫ P (φ) exp(iφ)dφ / ∫ P (φ) where P is the probability distribution of φ, the phase angle.

  • Rsym = Σh |I h 〈I h 〉|/Σh I h where 〈I h 〉 is the average intensity of reflection h for its symmetry and Friedel equivalents.

  • Rcullis = ( Σ|F PH ± F P | − F H(calc) / (Σ |F PH ± F P | ); phasing power = Σ |F H(calc) |/Σ||| F P | exp (iφc) + F H(calc) | − |F PH ||; anomalous phasing power = Σ |F H (i)| / Σ ||F PH (+) − F PH (−)| − 2F H(calc) sinφc | where F H(calc) is the calculated heavy atom structure factor, | F P| and |F PH| are the observed amplitudes for the protein and heavy atom derivatives respectively, φc is the experimental phase, F H (i) is the imaginary component of the calculated heavy atom structure factor, and F PH (+) and F PH (−) are observed amplitudes for Bijvoet pairs in heavy atom derivatives.

  • § R factor = ( Σ|F obs F calc |) / Σ ( F obs ) where F obs and F calc are the observed and calculated structure factors, respectively. R free is calculated in an analogous manner for 5% of the data that has never been used for refinement. Both values were calculated with no sigma cutoff.