Glial cell-line-derived neurotrophic factor (GDNF) is a protein known to enhance the survival of dopaminergic and motor neurons, It has been shown to have therapeutic potential in the treatment of Parkinson's disease and other neurodegenerative diseases. GDNF gene was modified by deletion and insertion mutagenesis using PCR. methods. The various mutants were all highly expressed in Escherichia coli. The recombinant proteins were purified and their survival-promoting activities were determined by motor neurons. The result showed that the C-terminus was critical for structure stability of GDNF, and the alpha-helix, finger1 and finger2 regions were involved in receptor binding, while the N-terminus was not essential for the biological functions of GDNF.