NMR, MOLECULAR MODELING, AND CRYSTALLOGRAPHIC STUDIES OF LENTIL LECTIN-SUCROSE INTERACTION

The conformational features of sucrose in the combining site of lentil lectin have been characterized through elucidation of a crystalline c omplex at 1.9-Angstrom resolution, transferred nuclear Overhauser effe ct experiments performed at 600 Mhz, and molecular modeling. In the cr ystal, the lentil lectin dimer binds one sucrose molecule per monomer. The locations of 229 water molecules have been identified. NMR experi ments have provided 11 transferred NOEs. In parallel, the docking stud y and conformational analysis of sucrose in the combining site of lent il lectin indicate that three different conformations can be accommoda ted. Of these, the orientation with lowest energy is identical with th e one observed in the crystalline complex and provides good agreement with the observed transferred NOEs. These structural investigations in dicate that the bound sucrose has a unique conformation for the glycos idic linkage, close to the one observed in crystalline sucrose, wherea s the fructofuranose ring remains relatively flexible and does not exh ibit any strong interaction with the protein. Major differences in the hydrogen bonding network of sucrose are found. None of the two inter- residue hydrogen bonds in crystalline sucrose are conserved in the com plex with the lectin. Instead, a water molecule bridges hydroxyl group s O2-g and O3-f of sucrose.