 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 2]](sx0041fig2mag.jpg)
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Figure 2
MNPG binding by cholera toxin. Superposition of the binding site of MNPG complexed with the B pentamer of two homologous toxins, LT and CT. The LTB–MNPG complex (green, PDB code 1lt6 ; Merritt et al., 1997  ) was superimposed onto the new structure of the CTB–MNPG complex (blue) by least-squares minimization of the coordinate difference for atoms C, N, CA, O, CB of conserved residues within 10 Å of one of the five independent binding sites (site F in this figure). The r.m.s. coordinate difference for the 157 superimposed atoms at this site was 0.30 Å. The only sequence difference between the two toxins in the immediate vicinity of the binding site is at residue 13, which is not involved in binding MNPG. (a) Electron-density contours at 4σ are shown from a σA-weighted omit map (mFo − Fc) of the CTB–MNPG complex at 2.0 Å resolution; the five copies of the ligand and all waters within 8 Å were omitted from the calculation of Fc. (b) Water molecules identified near all five binding sites have been superimposed back onto site F. Consensus water sites #1, #3 and #5 of the receptor-binding site are labeled (numbering as in Merritt, Sixma et al., 1994). The position of water Wat2 is occupied by O2′ of the nitrophenyl group. |
![[Figure 2]](sx0041fig2.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
