How overproduction of foreign proteins affects physiology of the recombinant strains of Hansenula polymorpha

Changes in the activity of key enzymes of the methanol utilization pathway of the recombinant strains of methylotrophic yeast Hansenula polymorpha R22-2B and LAC-56 were studied at different rates of chemostat growth on methanol containing mineral media. It was shown that the strain R22-2B, initially having a 10-fold increased activity of dihydroxyacetone kinase (DHAK, a key enzyme of formaldehyde assimilation) acquired increased activity of formaldehyde dehydrogenase (FADH, a key enzyme of formaldehyde dissimilation) which resulted in the enhanced oxidation of formaldehyde to CO2. Strain LAC-56, overproducing Escherichia coli beta-galactosidase, acquired the decreased intracellular concentration of ATP which resulted in the decrease of the efficiency of formaldehyde assimilation catalyzed by DHAK and resulted in accumulation of toxic formaldehyde. As a consequence some biochemical responses occurred in cells that were directed to a diminishing of the toxic effect of accumulated formaldehyde, namely, the decreasing of methanol oxidase activity (to reduce the rate of formaldehyde synthesis), and the increasing of FADH activity (to increase the rate of formaldehyde oxidation).