Crystal Structures of Endopolygalacturonase - Galacturonate Complexes at Atomic Resolution

Endopolygalacturonases are involved in the degradation of pectin by hydrolyzing the α-1, 4 glycosidic bonds. Crystal structure of endopolygalacturonase I from Stereum purpureum was solved at atomic (0.96 A) resolution. The enzyme folds into a right-handed parallel β-helix with 10 complete turns. The crystal structures of its binary complex with one D-galacturonate a and its ternary complex with two D-galacturonates were also determined at 1.0 and 1.15 A resolutions, respectively. The active site architecture of the complexes provides insight into the mode of substrate binding. These structures reveal that Asp 173 is the general-acid catalyst and, Asp 153 or Asp 174 is the general-base catalyst.