Methods and compositions related to the engineering of a protein with L-cyst(e)ine degrading enzyme activity are described. For example, in certain aspects there may be disclosed a modified cystathionine-γ-lyase comprising one or more amino acid substitutions and capable of degrading L-cyst(e)ine. Furthermore, certain aspects of the invention provide compositions and methods for the treatment of cancer with L-cyst(e)ine using the disclosed proteins or nucleic acids.