In-vivo half-life and hypoglycemic bioactivity of a fusion protein of exenatide and elastin-based polypeptide from recombinant Saccharomyces cerevisiae.

Exenatide (Ex) is a 39-amino acid peptide of glucagon-like peptide-1 (GLP-1) receptor agonist that was approved by the FDA in 2005 as a Type II diabetes treatment. It shows a 53% homology with GLP-1 but has an extended half-life (ca. 2.4 h) relative to GLP-1 (ca. 2-3 min). In this study, to further extend its in vivo half-life, we constructed a fusion protein (Ex-(EBP)-6xHis) using a biocompatible and inert elastin-based polypeptide (EBP) as a fusion partner. Valine was inserted into the guest position of the pentapeptide (VPGXG), no linker sequence was inserted in between the EBPs, and (EBP)-6xHis tag was attached to the C-terminus of exenatide. By using a recombinant Saccharomyces cerevisiae expression system, the fusion protein was expressed and secreted to the broth and purified by Ni-NTA affinity chromatography. Compared with the native exenatide, the physical half-life of the fusion protein was ca. 3.7-fold extended while approximately 72% of the in-vitro insulin secreting activity was maintained. However, the biological half-life measured by a glucose tolerance test (GTT) and the hypoglycemic test in mice was not significantly different from that of the native form. The effects of EBPylation on bioactivity and half-life of the fusion protein are similar to those of PEGylation. The result suggests that the bioactivity and half-life should be carefully balanced to obtain optimal fusion proteins. We expect that EBPylation using an optimal repeat number of EBP can be an alternative to chemical modification for therapeutic biobetters with extended half-life.