Improving specific activity and thermostability of Escherichia coli phytase by structure-based rational design

Escherichia coli phytase (EcAppA) which hydrolyzes phytate has been widely applied in the feed industry, but the need to improve the enzyme activity and thermostability remains. Here, we conduct rational design with two strategies to enhance the EcAppA performance. First, residues near the substrate binding pocket of EcAppA were modified according to the consensus sequence of two highly active Citrobacter phywtases. One out of the eleven mutants, V89T, exhibited 17.5% increase in catalytic activity, whichmight be a result of stabilized protein folding. Second, the EcAppA glycosylation pattern was modifiedin accordance with the Citrobacter phytases. An N-glycosylation motif near the substrate binding sitewas disrupted to remove spatial hindrance for phytate entry and product departure. The de-glycosylatedmutants showed 9.6% increase in specific activity. On the other hand, the EcAppA mutants that adopt Nglycosylation motifs from CbAppA showed improved thermostability that three mutants carrying singleNglycosylation motif exhibited 5.6-9.5% residual activity after treatment at 80. C (1.8% for wild type). Furthermore, the mutant carrying all three glycosylation motifs exhibited 27% residual activity. In conclusion, a successful rational design was performed to obtain several useful EcAppA mutants with betterproperties for further applications. (C) 2014 Elsevier B. V. All rights reserved.