| Summary: | Today, recombinant expression of proteins is used for a variety of purposes. One of these is the production of allergens, which are vital components in allergy diagnostics. However, traditional expression systems such as Escherichia coli and Pichia pastoris might not have the capacity to express all proteins of interest. Thermo Fisher, which is a leading producer of allergy tests, has requested an evaluation of different microorganisms and their capacity for heterologous protein expression in order to expand their existing toolbox of expression systems. This summary was made through a literature study, where twelve organisms were evaluated. Six eukaryotic and six prokaryotic expression systems are compared based on their ability to properly glycosylate protein, need for specific culture conditions, safety, protease activity, duration, protein yield and protein solubility. The prokaryotic systems – Corynebacterium glutamicum , Lactococcus lactis , Pseudomonas fluorescens , Pseudoalteromonas haloplanktis , Ralstonia eutropha and Streptomyces lividans – are characterized by being easy to cultivate, operating in different temperature ranges and providing relatively high yields of recombinant protein. The eukaryotic systems – Aspergillus fungi, the green algae Chlamydomonas reinhardtii , the yeast Hansenula polymorpha , the parasite Leishmania tarentolae , the moss Physcomitrella patens and suspension-based plant cells – all have very different morphology and properties. In comparison with the prokaryotic systems, it can be concluded that they are generally better at folding and providing the correct glycosylation patterns for mammalian and plant proteins. However, they require more time and effort to establish a competent cell line. Furthermore, the resulting protein yield is usually less than for the prokaryotic systems. The conclusion can be drawn that no expression system is perfect. The solution is a toolbox, containing various expression systems and vector systems, providing the basis for successful expression of all kinds of complex proteins. Based on the evaluation of expression systems in this review, such toolbox can be obtained.
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