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The novel Fh8 and H fusion partners for soluble protein expression in Escherichia coli: a comparison with the traditional gene fusion technology


The Escherichia coli host system is an advantageous choice for simple and inexpensive recombinant protein production but it still presents bottlenecks at expressing soluble proteins from other organisms. Several efforts have been taken to overcome E. coli limitations, including the use of fusion partners that improve protein expression and solubility. New fusion technologies are emerging to complement the traditional solutions. This work evaluates two novel fusion partners, the Fh8 tag (8 kDa) and the H tag (1 kDa), as solubility enhancing tags in E. coli and their comparison to commonly used fusion partners. A broad range comparison was conducted in a small-scale screening and subsequently scaled-up. Six difficult-to-express target proteins (RVS167, SPO14, YPK1, YPK2, Frutalin and CP12) were fused to eight fusion tags (His, Trx, GST, MBP, NusA, SUMO, H and Fh8). The resulting protein expression and solubility levels were evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis before and after protein purification and after tag removal. The Fh8 partner improved protein expression and solubility as the well-known Trx, NusA or MBP fusion partners. The H partner did not function as a solubility tag. Cleaved proteins from Fh8 fusions were soluble and obtained in similar or higher amounts than proteins from the cleavage of other partners as Trx, NusA or MBP. The Fh8 fusion tag therefore acts as an effective solubility enhancer, and its low molecular weight potentially gives it an advantage over larger solubility tags by offering a more reliable assessment of the target protein solubility when expressed as a fusion protein.

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The financial support of the EMBL Heidelberg, Germany and Fundação para a Ciência e Tecnologia (FCT), Portugal, is acknowledged: the fellowship SFRH/BD/46482/2008 to Sofia J. Costa and the project PTDC/CVT/103081/2008. The authors wish to acknowledge Anne-Claude Gavin for providing four of the constructs for this study (RVS167, SPO14, YPK1, and YPK2) and Emmanuel Poilpré for the experimental help (both from the EMBL Heidelberg, Germany).

Competing interests

The Fh8 tag utilization for the improvement of protein soluble expression in E. coli is covered by a worldwide patent (WO 2010082097) licensed to Hitag Biotechnology, Lda. The authors S.C., A.A., and A.C. are coowners of the patent and are associated with Hitag Biotechnology, Lda.

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Correspondence to Lucília Domingues.

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Costa, S.J., Almeida, A., Castro, A. et al. The novel Fh8 and H fusion partners for soluble protein expression in Escherichia coli: a comparison with the traditional gene fusion technology. Appl Microbiol Biotechnol 97, 6779–6791 (2013).

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  • Escherichia coli
  • Fusion protein
  • Fh8 fusion tag
  • Traditionally used fusion tags
  • Protein solubility
  • Tag removal