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
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.