Structural studies on peanut lectin complexed with disaccharides involving different linkages: further insights into the structure and interactions of the lectin

Crystal structures of peanut lectin complexed with Gal$_\beta$ 1-3Gal, methyl-T-antigen, Gal$_\beta$1-6Gal\alpha NAc, Gal\alpha1-3Gal and Gal\alpha1-6Glc and that of a crystal grown in the presence of Gal\alpha1-3Gal$_\beta$1-4Gal have been determined using data collected at 100 K. The use of water bridges as a strategy for generating carbohydrate specificity was previously deduced from the complexes of the lectin with lactose (Gal$_\beta$1-4Glc) and T-antigen (Gal$_\beta$1-3GalNAc). This has been confirmed by the analysis of the complexes with Gal$_\beta$1-3Gal and methyl-Tantigen (Gal$_\beta$1-3GalNAc-\alpha-OMe). A detailed analysis of lectin–sugar interactions in the complexes shows that they are more extensive when the $_\beta$-anomer is involved in the linkage. As expected, the second sugar residue is ill-defined when the linkage is $1\rightarrow 6$. There are more than two dozen water molecules which occur in the hydration shells of all structures determined at resolutions better than 2.5 \AA. Most of them are involved in stabilizing the structure, particularly loops. Water molecules involved in lectin–sugar interactions are also substantially conserved. The lectin molecule is fairly rigid and does not appear to be affected by changes in temperature.