Compositions and methods for protecting a plant from an insect pest are provided. The invention provides mutagenized nucleic acids that have been engineered to encode pesticidal polypeptides having increased resistance to proteolytic degradation by a plant protease. In particular, nucleic acid sequences encoding pesticidal polypeptides modified to comprise a proteolytic protection site that confers resistance to degradation or proteolytic inactivation by a plant protease are provided. Particular embodiments of the invention provide expression cassettes and transformed plants, plant cells, and seeds. These compositions find use in methods for protecting a plant from a pest.