Table 1. X-ray crystallographic data and final protein plus ligand model-refinement statistics for both the cisplatin and carboplatin crystals.

Values in parentheses are for the last shell.

	Cisplatin/NaI	Carboplatin/NaI
PDB code	4ow9	4owa
Data-collection temperature (K)	100	100
Data reduction
Space group	P21	P21
Unit-cell parameters (Å, °)	a = 27.25, b = 62.54, c = 58.98, β = 90.92	a = 27.14, b = 62.28, c = 58.05, β = 92.59
Molecules per asymmetric unit	2	2
Observed reflections	110261	104255
Unique reflections	11636	20257
Resolution (Å)	31.27–2.10 (2.15–2.10)	29.04–1.80 (1.90–1.80)
Completeness (%)	90.1 (55.7)	94.3 (78.0)
R merge (%)	0.130 (0.229)	0.099 (0.340)
〈I/σ(I)〉	11.7 (3.5)	11.7 (1.9)
Multiplicity	6.9 (1.6)	5.7 (1.4)
Refinement
Cruickshank DPI (Å)	0.11	0.18
No. of atoms
Protein	2002	2002
Water molecules	39	147
Pt and halogen atoms	34	42
Other bound atoms	28	28
Average B factor (Å2)
Protein atoms	21.1	12.2
Water molecules	18.8	19.2
Pt and halogen atoms	29.1	20.9
Other bound atoms	24.8	18.4
R factor/R free (%)	19.7/27.1†	18.4/24.0
R.m.s.d., bonds (Å)/angles (°)	0.010/1.5	0.015/1.6
Ramachandran values (%)
Most favoured	94.1	96.5
Additional allowed	5.2	3.1
Disallowed	0.8‡	0.4‡

^†The PDB validation report includes phenix.xtriage statistics; subsequent use of DETWIN in CCP4 suggested that the data were 6% twinned. To our knowledge, no twinning has been reported for this form of HEWL in NaI conditions before. Turning on amplitude twin refinement in REFMAC improved the R/R _free from 19.7/27.5% to 19.7/27.1%. The electron-density maps at the His binding sites as well as in general were the same with and without using twin refinement, presumably owing to the rather small twin fraction.

^‡The disallowed residues are Asp18, Ser72 and Arg73 and are part of a loop/turn region.