CONSERVED WATERS IN LEGUME LECTIN CRYSTAL-STRUCTURES - THE IMPORTANCEOF BOUND WATER FOR THE SEQUENCE-STRUCTURE RELATIONSHIP WITHIN THE LEGUME LECTIN FAMILY

An analysis of the water structure in the crystals of different legume lectins has been carried out. Protein hydration is found to be mainly dependent on the detailed local surface characteristics of the protei n and will adapt upon the limited conformational changes that are the resultant of crystal packing forces and point mutations. Yet a signifi cant portion of the water positions determined by x-ray crystallograph y appears to be conserved in all independent crystal structures of a g iven protein. Some of these waters are specific to this one specific p rotein, while others are conserved in crystal structures of homologous proteins as well. For those conserved waters, a clear structural role is often evident. Seven water sites were found to be completely conse rved in all legume lectin crystal structures, independent of their deg ree of sequence homology or carbohydrate specificity. Of these, four w aters are ligands to the manganese and calcium ions, and one water is located in the saccharide binding site interacting with a conserved As p and Asn residue. Of the remaining two conserved waters, one of them stabilizes a beta-hairpin, while the other interacts with a beta-bulge structure of the back sheet.