Enhancement of the yield of long helical structure of recombinant nucleocapsid protein of Newcastle disease virus

► Western blot image analysis was used to predict proteases cleavage sites ofNPΔc375. ► PeptideCutter program was used to identify the protease that attacking NPΔc375. ► Metallo- and serine-proteases were predicted as the protease that attacking NPΔc375. ► EDTA and PMSF were used to inhibit activities of metallo- and serine-proteases. ► The particle assembly property and antigenicity of treated NPΔc375 were retained.