Baculovirus infection of Sf9 cells at high densities, such as during mid- and late exponential phase, often results in a significant reduction of protein yield per cell, compared to the early exponential phase. Nutrient depletion has been considered as a major cause for the decreased protein yield. In this study, we report that the addition of nutrients (glucose, yeastolate ultrafiltrate, and lactalbumin hydrolysate) and small fraction of fresh medium at time of infection restores the expression level of actin and myosin V–HMM at late exponential phase (11.3 × 106 cells/ml) to that at early exponential phase (1.0 × 106 cells/ml). The relative yields of actin and myosin V–HMM were approximately equal at both phases (typically 200 mg of actin and 5 mg of myosin V–HMM per 1010 cells), i.e., the volumetric yield of proteins from the cell culture at late exponential phase was approximately tenfold higher than at early exponential phase. The functionality of the recombinant actin and myosin V–HMM was confirmed by measuring the rate of actin polymerization, actin-activated ATPase, and the gliding velocity of actin filaments in an in vitro motility assay.
Actin Baculovirus Myosin V Insect cell High-density culture Nutrient feeding
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This work was supported by the Grants-in-Aid for Specially Promoted Research and Scientific Research (S) from the Ministry of Education, Culture, Sports, Science and Technology of Japan to S.I.
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