Expression, fermentation, purification and lyophilisation of recombinant Subtilisin QK in Pichia pastoris

•A high expressed strain GS115/pPICZαA–QK was constructed with optimized QK gene.•The thrombolytic activity reached 112,000IU/mL at the end of fermentation.•After HIC and GFC purification, the purity of QK was 95%.•The addition of 5% trehalose could maintain 94.2% thrombolytic activity after FD.