Andreas Kirschning and colleagues from Leibniz Universität Hannover, Germany, have developed a microreactor concept based on their recently reported PASSflow (polymer-assisted solution phase synthesis under flow conditions) system, showing how it can be used for the purification and immobilisation of tagged proteins. In the interview below, Kirschning explains the significance of the work. 

1. Could you explain to the non-specialist the significance of your article? 

Immobilized enzymes are of great interest and importance in chemoenzymatic synthesis, due to high stability, easy product isolation and enzyme recovery. One major drawback is the limited portfolio of methods for a fast and reliable immobilization of the enzymes. Additionally enzymes have to be purified prior to immobilization. The article introduces a reactor design, which is based on Ni-NTA chelation. This method allows a selective and fast immobilization of proteins using crude protein extracts. The immobilized enzymes are then directly used for a variety of enzymatic syntheses. Using this technique it is possible to obtain ready-to-use enzyme reactors within minutes starting from crude protein mixtures. 

2. What has motivated you to conduct this work? 

This work was done to further advance the applicability of microreactor technology, specifically our PASSflow concept, from chemical synthesis to chemoenzymatic and purely enzymatic synthesis. Additionally, we wanted to develop a patent free NTA-linker which could be broadly applied. 

3. Where do you see this work developing in the future?

With reactor development and proof of principle - both covered by this paper - we paved the way for broad utilization of this reactor system using enzymatic catalysis in the flow-through mode. In addition to established systems (here mainly membrane reactors and classically immobilized enzymes) this technique will be applied when a fast and mild immobilisation of over-expressed proteins is mandatory. Presently, the enzymatic synthesis of a biopolymer, namely polysialic acid, is targeted using this reactor design. 

4. Are there any particular challenges facing future research in this area? 

Further automation and application for a variety of proteins is one challenge. Introduction of even more specific binding motifs (e.g. streptavidin instead of Ni-NTA) will be a major challenge.