FIGURE 4.

Carbohydrate-binding pocket of CNL with bound lactose (A) and LDN (B) is shown. The sugars are presented as stick models. The amino acid residues involved in the formation of hydrogen bonds (shown as orange dashed lines) are labeled. C, superimposition of α-, β-, and γ-repeats of CNL. The repeats are shown in yellow, blue, and green, respectively. The amino acid residues involved in hydrogen bond formations in α-repeat are labeled and colored yellow, and structurally equivalent residues in β- and γ-repeats (see Fig. 5) are colored blue and green, respectively. It is evident that, in contrast to Asp²⁰ in the α-repeat, the corresponding Arg⁷² in β- and Thr¹¹⁶ in γ-repeats cannot serve as the anchoring point for a lactose molecule.