High-level synthesis of the 12-kDa human FK506-binding protein in Escherichia coli using translational coupling

The gene encoding the 12-kDa cytosolic form of human FK506-binding protein (hFKBP-12) was isolated from a Jurkat T-cell cDNA library and expressed in three different non-fusion systems in Escherichia coli. Expression of recombinant hFKBP-12 (re-hFKBP-12) from the trc promoter vector, pKK233-2, yielded low levels of protein. A second system, which utilized a modified lac promoter and a stronger ribosome-binding site, showed greatly improved expression. A third system, utilizing translational coupling to an upstream segment of kdsB under the control of this modified lac promoter, produced re-hFKPB-12 at a very high level. The re-hFKBP-12 produced via translational coupling was soluble and was shown to have the authentic N terminus. The level of active re-hFKPB-12 produced from this vector was estimated to be 50% of total soluble protein, based on competition with the fusion protein, CKS::re-hFKBP-12, for binding to ascomycin-C22-carboxymethyloxime-alkaline phosphatase.