FIGURE 3.

CRT undergoes limited conformational changes upon carbohydrate binding. A, overlay of unliganded (yellow) and Glc₁Man₃-bound (green) CRT lectin domain structures shows differences in the large loop between strands β6 and β7. B, the conformation of the loop in unliganded CRT is stabilized by hydrogen bonds between the side chain of Asp³¹⁷ and amides of Gly¹²⁴ and Asp¹²⁵ and between the side chain of Lys¹¹¹ and carbonyl of Asp¹²⁵. C, in the complex, sugar residues Glc(3) and Man(D1) engage loop residues Gly¹²⁴ and Asp¹²⁵ through a 60 ° rotation in the ψ backbone angle of Gly¹²⁴. This rotation enables the side chain of Asp¹²⁵ to participate in carbohydrate binding via an ordered water molecule (cyan sphere). The interactions of Asp³¹⁷ with Gly¹²⁴ are replaced by hydrogen bonds of Asp³¹⁷ with Man(D1).