Continuous matrix-assisted refolding of proteins

A refolding reactor was developed for continuous matrix-assisted refolding of proteins. The reactor was composed of an annular chromatography system and an ultrafiltration system to recycle aggregated proteins produced during the refolding reaction. The feed solution containing the denatured protein was continuously fed to the rotating bed perfused with buffer promoting folding of the protein. As the protein passed through the column, it was separated from chaotropic and reducing agents and the refolding process took place. Native proteins and aggregates could be continuously separated due to different molecular size. The exit stream containing aggregates was collected, concentrated by ultrafiltration and recycled to the feed solution. The high concentrations of chaotropic and reducing agents in the feed solution enabled dissociation of the recycled aggregates and consequently were fed again to the refolding reactor. When the initial feed mixture of denatured protein is used up, only buffer-containing chaotropic agents and recycled aggregates are fully converted to native protein. This process resulted in a stoichiometric conversion from the denatured protein to its correctly folded native state. The system was tested with bovine α-lactalbumin as model protein. Superdex 75 PrepGrade was used as size-exclusion medium. The yield of 30% active monomer in the batch process was improved to 41% at a recycling rate of 65%. Assuming that the aggregates can be redissolved and recycled into the feed stream in a quantitative manner, a refolding yield close to 100% is possible. The method can be also applied to other chromatographic principles suited for the separation of aggregates.