1 Crystal Structure of Banana Lectin Reveals a Novel Second Sugar Binding Site

ow nloaded from 2Abstract Banana lectin is a dimeric plant lectin from the jacalin-related lectin family. Banana lectin belongs to a subgroup of this family that binds to glucose/mannose, but is unique in recognizing internal 1,3 linkages as well as 1,3 linkages at the reducing termini. Here we present the crystal structures of banana lectin alone and with laminaribiose (Glc1,3Glc) and Xyl-1,3-Man--O-Methyl. The structure of banana lectin has a -prism-I fold, similar to other family members, but differs from them in its mode of sugar binding. The reducing unit of the sugar is inserted into the binding site causing the second saccharide unit to be placed in the opposite orientation compared to the other ligand-bound structures of family members. More importantly, our structures reveal the presence of a second sugar-binding site that has not been previously reported in the literature. The residues involved in the second site are common to other lectins in this family, potentially signaling a new group of mannose-specific jacalin-related lectins with two sugar binding sites