Construction and characterization of a functional variant hFGF7 with enhanced properties by circular permutation

Human fibroblast growth factor 7 (hFGF7) is a member of the paracrine-acting FGF family and mediates various reactions such as wound healing, tissue homeostasis, and liver regeneration. These activities make it a plausible candidate for pharmaceutical applications as a drug. However, the low expression level and stability of the recombinant hFGF7 were known to be major hurdles for further applications. Here, we attempted to improve the expression level and stability of hFGF7 by changing the order of amino acids through circular permutation (CP), thereby expecting an alternative fate according to N-end rules. CP-hFGF7 variants were constructed systematically by using putative amino acid residues in the loop region that avoided the disruption of the structural integrity especially in the functional motif. Among them, cp-hFGF7 revealed a relatively higher expression level in the soluble fraction than the wild-type hFGF7 and was efficiently purified to apparent homogeneity by three consecutive steps. Approximately, 7 mg of the purified protein was obtained from a 1 L culture and showed a comparable activity to that of the wild type hFGF7. In addition, the spectral properties related to the apparent structure of cp-hFGF7 were quite similar to those of the wild type hFGF7. Therefore, CP could be an alternative tool for the functional expression of hFGF7 in Escherichia coli .