Soluble expression, purification, and secondary structure determination of human PDX1 transcription factor.

The transcription factor PDX1 is a master regulator essential for proper development of the pancreas, duodenum and antrum. Furthermore, it is an indispensable reprogramming factor for the derivation of human β-cells, and recently, it has been identified as a tumor suppressor protein in gastric cancer. Here, we report the soluble expression and purification of the full-length human PDX1 protein from a heterologous system. To achieve this, the 849 bp coding sequence of the PDX1 gene was first codon-optimized for expression in Escherichia coli (E. coli). This codon-optimized gene sequence was fused to a protein transduction domain, a nuclear localization sequence, and a His-tag, and this insert was cloned into the protein expression vector for expression in E. coli strain BL21(DE3). Next, screening and identification of the suitable gene construct and optimal expression conditions to obtain this recombinant fusion protein in a soluble form was performed. Further, we have purified this recombinant fusion protein to homogeneity under native conditions. Importantly, the secondary structure of the protein was retained after purification. Further, this recombinant PDX1 fusion protein was applied to human cells and showed the ability to enter the cells as well as translocate to the nucleus. This recombinant tool can be used as a safe tool and can potentially replace its genetic and viral forms in the reprogramming process to induce a β-cell-specific transcriptional profile in an integration-free manner. Additionally, it can also be used to elucidate its role in cellular processes and for structural and biochemical studies.