Atomic models of (1→3)-β-glucans. (a) The carbohydrate molecules bound in the catalytic cleft of the present 1,3-β-glucanase in the 7G complex. Electron density is shown as an Fo − Fc OMIT map (green) contoured at 2.5σ. The models in orange represent the glucose units built in electron-density maps and included in the coordinate set; the two units of the tetrasaccharide shown in grey (+1 and +2) are not part of the crystallographic model because of disorder and have been tentatively placed in the visible electron density in the binding groove only for the purpose of this figure (and Fig. 7) to illustrate the length and general shape of the ligand in subsites +1 to +4. (b) A heptamer modelled by Bohne et al. (1999) using SWEET2 (yellow) superposed on the nonreducing end of the trisaccharide of the present 7G complex.