Technologies to keep an eye on: alternative hosts for protein production in structural biology

The conduct of many trials for the successful production of large quantities of pure proteins for structural biology and biotechnology applications, particularly of active, authentically processed enzymes, large eukaryotic multi-subunit complexes and membrane proteins, has spurred the development of recombinant expression systems. Beyond the well-established Escherichia coli, mammalian cell culture and baculovirus-infected insect cell expression systems, a plethora of alternative expression systems has been discovered, engineered, matured and deployed, resulting in crystal, nuclear magnetic resonance, and electron microscopy structures. In this review, we visit alternative expression hosts for structural biology ranging from bacteria and archaea to filamentous and unicellular yeasts and protozoa, with particular emphasis on their applicability to the structural determination of high-value, challenging proteins and complexes.