Polymer nanodiscs support the functional extraction of an artificial transmembrane cytochrome

Polymer nanodiscs are an attractive alternative to surfactants for studying integral membrane proteins within their native lipid environment. Here, we investigate the use of such polymers to isolate a computationally-designed de novo membrane cytochrome named CytbX. We show that the block copolymers known as CyclAPols can efficiently extract CytbX directly from biomembranes and are compatible with the downstream purification and biophysical characterisation of this artificial protein. CyclAPol-solubilised CytbX is well-folded and highly robust with properties that are essentially identical to those observed for the same protein in a detergent micelle. However, electron transfer to CytbX from a diffusive flavoprotein is substantially faster in micelles than in the nanodisc system. Our results confirm that polymer nanodiscs will be a useful tool for the ongoing study and application of de novo membrane proteins.