High cell density fed-batch production of insecticidal recombinant ribotoxin hirsutellin A from Pichia pastoris

BackgroundThe fungal ribotoxin hirsutellin A (HtA) exhibits strong insecticidal activity; however, efficient systems for expressing recombinant HtA (rHtA) are lacking. Here, we established an efficient heterologous expression system to produce large amounts of rHtA.ResultsRecombinant Pichia pastoris transformants with high levels of secretory rHtA were screened, and in a fed-batch reactor, rHtA was secreted at levels up to 80mg/l following methanol induction, which was more than sixfold higher than that in shake flasks. Approximately 7mg of highly pure rHtA was obtained from 300ml of fed-batch culture supernatant by Ni+-nitriloacetic acid affinity chromatography and CM Sepharose ion-exchange chromatography. Mass spectrometry results revealed rHtA as a native N-terminal non-glycosylated monomeric protein with a molecular weight of 15.3kDa. Purified rHtA exhibited excellent thermal and protease stability and dose-dependent cytotoxicity to Sf9 insect cells and insecticidal activity against Galleria mellonella larvae.ConclusionsThis is the first report of rHtA expression in P. pastoris. The rHtA was expressed at a high level under high-cell-density fed-batch fermentation and was efficiently purified using a two-step purification method. Purified rHtA exhibited thermal and protease stability, as well as appropriate bioactivities. Our results indicate that fed-batch production by P. pastoris is an efficient method to produce functional rHtA.