Disruption of hexokinase II (HXK2) partly relieves glucose repression to enhance production of human kringle fragment in gratuitous recombinant Saccharomyces cerevisiae

The GAL1 gene encoding galactokinase was disrupted in a recombinant Saccharomyces cerevisiae strain in which production of LK8 protein, a kringle fragment of human apolipoprotein, is under the control of GAL1 promoter. Null mutation of the HXK2 gene was introduced further in the gal1Delta strain to relieve glucose repression. A pattern for LK8 expression was compared for the two recombinant S. cerevisiae systems in continuous and fed-batch cultivations. A critical dilution rate in continuous cultivation that repressed LK8 expression was significantly higher for the gal1Deltahxk2Delta strain than that for the gal1Delta strain to sustain the LK8 production even at high glucose consumption rate. Expressed LK8 for the gal1Delta strain was not detectable when the dilution rate exceeded 0.05 h(-1). Maximum LK8 concentration of 57 mgl(-1) was obtained in glucose-limited fed-batch cultivation of the gal1Deltahxk2Delta strain, corresponding to a 13.8-fold enhancement compared with the gal1Delta strain grown under the same conditions.