The influence of protein refolding strategy on cost for competing reactions

Abstract

Protein refolding is a key operation in many bioprocesses utilizing Escherichia coli. Most laboratory studies into refolding are conducted in batch systems at "infinite" dilution to avoid the formation of aggregates. This policy will be grossly suboptimal if adopted for scale-up. The impact of refolding policy on dimensionless annual operating cost for a simplified kinetic scheme is therefore investigated in this work. For competing refolding and aggregation in a continuous stirred-tank reactor, high conversion (X> 99.9%) and high dimensionless concentration minimize the annual cost. However, this policy results in a significant cost penalty when the native protein is in equilibrium with an aggregating intermediate. In such cases, a distinct optimal conversion and concentration exist. The precise location of the optimum depends on the extent of the back reaction, with a trend to lower conversions and concentrations as the equilibrium distribution shifts towards the intermediate. This work highlights the need to establish critical design parameters at an early stage in the scale-up of bioprocesses involving refolding. It also highlights the need to optimize the process in a global rather than unit-wise fashion.