Protein expression in bacteria is a common method to obtain high quantities of proteins. It is used in the industry and research to a great extent, however some recombinant proteins are hard and tedious to express in bacteriaâs. Factors that impact this can be size, toxicity or folding properties. Prokaryotes are not optimized to fold all recombinant proteins and this is preventing high protein yields. However, when the concentration of chaperone are modified; the obtained protein yield are changes. Co-expression of chaperones is there for a way to modify the yield of natively folded proteins (1). The goal of LiU iGEM 2018 is therefore to investigate the folding process and the necessity of chaperones by creating and expressing our own chaperone plasmids containing GroES in E. coli.
Background
Chaperones assist the protein folding in all organisms. They do this by interacting in different subsystems that targets different problems of the folding pathway.
This year we focused on the GroE-system, and more specifically the chaperone GroES. GroES is a co-chaperone that is known to interact with the GroEL chaperone, and turn misfolded and unfolded proteins into natively folded proteins. However, it is hypothesised that GroES can interact with a substrate protein on its own. The thought being that GroES acts as a holdas and there by prohibits unfolded proteins from interacting with aggregates (2).
How do we plan to solve the project?
Our project revolves around creating a chaperone plasmid containing the chaperone GroES. The chaperone will then be utilized in co-expression with the difficult to express proteins. Co-expression is essential in order to enable easy and sufficient protein expression of different proteins. The idea is not a groundbreaking one, e.g. Takara created chaperone plasmids that can be used similarly (3). However, our plasmid can be co-expressed both alongside a client protein, but also in combination with Takara plasmids and the client protein. This was done by placing GroES in a plasmid with a C class Origin of replication. More specifically pSB_4A5. This enables co-expression with all B class plasmids, like for instance Takara plasmids. Or co-expression with A class plasmids, like pSB_1C3.
Applications
Our project illustrates the necessity of chaperones, more specifically GroES, in protein production. Our plasmid could be utilized in research purposes of neurodegenerative diseases, and also in other fields where a higher and more correctly folded amount of protein is needed such as industrial protein production. We showed that our part can enhance the expression of the aggregation-prone florescent fusion protein such as EGFP-Ađ· 1-42 and mNG-Ađ· 1-42. Similar results could be achieved when co-expressing other proteins. Our part can also be combined with the Takara plasmids as an add on. The co-expression of chaperones also gives insight into the folding pathway of the client proteins.
References
1. Rosano GL, Ceccarelli EA. Recombinant protein expression in Escherichia coli: advances and challenges. Front Microbiol. 2014;5:172.
2. Moparthi SB, Sjölander D, Villebeck L, Jonsson B-H, Hammarström P, Carlsson U. Transient conformational remodeling of folding proteins by GroESâindividually and in concert with GroEL. J Chem Biol. 2014;7(1):1â15.
3. Chaperone Plasmid Set For Research Use v201701Da [Internet]. [cited 2018 Aug 12]. Available from: http://www.takara-bio.com
