Structural restoration of inactive recombinant fish growth hormones by chemical chaperonin and solvent restraint approaches

Recombinant proteins may undergo conformational distortion, leading to aggregation and loss of function, when they are expressed in heterologous systems. The structural and functional restoration of such inactive proteins is highly desirable. We have over-expressed recombinant growth hormones from the fish ayu (Plecoglossus altivelis) and yellow grouper (Epinephelus awoara) by a pET expression system. Both recombinant proteins accumulate as insoluble form in Escherichia coli. We refolded these inactive proteins into the active form using a stepwise refolding process with a dilute denaturing agent as a steric blocker and chemical chaperonin. Optical characterization showed that stable folding intermediates with a helical conformation can be detected in the molten globule state. Moreover, the function of restored recombinant growth hormones was demonstrated by its ability to stimulate proliferation in zebrafish liver cells.