Abstract
Human fibroblast growth factor 19 (hFGF19) is a difficult-to-express protein that is frequently fused with another protein for soluble expression. However, residual amino acids after cleavage with protease represent one of the major problems in therapeutic protein development. Here, we introduced synonymous codon substitutions in the N-terminal region encoding sequence of hFGF19 and co-expressed disulfide bond isomerase (ΔssDsbC) to functionally express hFGF19 without any fusion protein. Synonymous codon substitution significantly increased hFGF19 expression. Subsequent co-expression of ΔssDsbC with a selected variant of hFGF19 (scvhFGF19) further increased the proportion of soluble hFGF19 expression in Escherichia coli XL1-Blue. Both total and soluble scvhFGF19 expression increased remarkably in the alternative host, E. coli Origami 2 with mutated thioredoxin reductase and glutathione reductase. scvhFGF19 purification by anion exchange and heparin affinity chromatography resulted in a yield of 6.5 mg/L under normal induction conditions in flask culture. As such, a high cell density culture is expected to achieve an even higher yield. The biological activities of purified scvhFGF19 were assessed based on its ability to activate ERK1/2 signaling pathway in HepG2 hepatocarcinoma cells. In conclusion, the strategy described here may represent an efficient alternative process for the production of hFGF19 and/or related proteins.
Highlights
Fibroblast growth factor (FGF) is a representative growth factor that activates various signaling pathways by binding to fibroblast growth factor receptors (FGFRs) [1]
We speculated that marginal soluble expression of scvhFGF19 was probably associated with structural features such as the two internal disulfide bonds and the long, disordered region at the N- and C-terminus [12]
As the reducing environment of the E. coli cytoplasm is unfavorable for the formation of disulfide bonds, correct folding of scvhFGF19 may be impaired
Summary
Fibroblast growth factor (FGF) is a representative growth factor that activates various signaling pathways by binding to fibroblast growth factor receptors (FGFRs) [1]. The hFGF family proteins are classified into seven groups based on phylogenetic analysis as well as intracrine, paracrine, and endocrine FGFs based on their mechanisms of action [4]. Recent advances in molecular biological tools, such as fusion proteins and genetically modified hosts, have facilitated functional expression of this difficult-to-express protein in the cytoplasm of E. coli, the host environment is unfavorable for the formation of disulfide bonds [8]. Fusion proteins or tags are frequently used to facilitate soluble expression and purification of recombinant proteins. Removal of these fusion proteins without any scar (amino acids remaining after digestion with protease) is difficult. The functional expression of hFGF19 without any fusion tag or protein has not yet been reported in E. coli
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