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Structural insights into the processivity of endopolygalacturonase I from Aspergillus niger
Gertie van Pouderoyen1, Harm J Snijder, Jacques A E Benen
1Laboratory of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Abstract:
Endopolygalacturonase I is a processive enzyme, while the 60% sequence identical endopolygalacturonase II is not. The 1.70 A resolution crystal structure of endopolygalacturonase I reveals a narrowed substrate binding cleft. In addition, Arg96, a residue in this cleft previously shown to be critical for processivity, interacts with the substrate mimics glycerol and sulfate in several well-defined conformations in the six molecules in the asymmetric unit. From this we conclude that both Arg96 and the narrowed substrate binding cleft contribute to retaining the substrate while it moves through the active site after a cleavage event has occurred.