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![[Figure 4]](ei5025fig4mag.jpg)
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Figure 4
(a) The asymmetric unit contents showing four molecules of Cel5A (PDB code 3mmw; Pereira et al., 2010  ). (b) The Cel5A structure showed that cadmium was essential to form `bridges' across the interface of protein molecules through coordination by the negative charge residue Glu99 present at the surface of the protein. A 2mFo–DFc electron density map contoured at 1.5σ is shown in blue around the Glu99 residues and an mFo–DFc electron density map contoured at 10σ when the divalent metal was omitted from the model is shown in black around Cd2+. (c) The presence of Ni2+ and Cd2+ produced Cel5A crystals belonging to the P1 space group that were solved at 2.2 Å resolution. The crystallization condition of these crystals was 0.02 M nickel(II) chloride, 0.02 M magnesium chloride, 0.02 M cadmium chloride, 0.1 M sodium acetate trihydrate pH 4.5 and 16% polyethylene glycol monomethyl ether 2000. (d) When only Cd2+ was included in the crystallization solution, Cel5A crystals belonging to the P21 space group were produced with a completely different crystal morphology, which were solved at 1.8 Å resolution. The crystallization condition for the Cel5A P21 crystals was 0.02 M cadmium chloride, 0.1 M sodium acetate trihydrate pH 4.5 and 16% polyethylene glycol monomethyl ether 2000 (Pereira et al., 2010). |
![[Figure 4]](ei5025fig4.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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