Aggregation-driven expression of liraglutide precursors using engineered mini-tags in Escherichia coli

Glucagon-like peptide-1 (GLP-1), a 31-amino acid incretin hormone, is widely used in the treatment of type 2 diabetes mellitus due to its glucose-dependent insulinotropic activity. However, its small size makes it highly prone to proteolytic degradation in microbial expression systems such as Escherichia coli, leading to reduced manufacturing yield. While fusion to cleavable protein tags can improve peptide stability during purification, excessively large tags often compromise the overall yield, especially when the target peptide is smaller than the fusion partner. To overcome this limitation, we have engineered 11 cleavable fusion tag constructs (LP1-LP11) for recombinant expression of Arg34-GLP-1(7-37) (liraglutide precursor) in E. coli. The 11 constructs differed only in the tags. The expression vector contained a T7 leader sequence, affinity tags (6×His/6×Arg), inclusion body tags (11-125 amino acids), and TEV protease cleavage sites. Among the 11 tags, LP8 with a compact 4.0 kDa tag achieved the highest expression, yielding 133 mg/L of fusion protein and a calculated liraglutide precursor yield of 60 mg/L based on mass fraction (45% of fusion mass), with an actual recovered yield of 14.6 mg/L after RP-HPLC purification, largely due to efficient inclusion body formation (>95% insolubility) and enhanced translational initiation driven by the T7 leader sequence. The purified peptide's identity and sequence integrity were confirmed by LC/MS analysis. The primary advantage of this approach is mass fraction optimization which focuses on minimizing fusion-tag mass to maximize yield relative to the tag size without compromising inclusion-body formation thereby providing a scalable and economical approach for GLP-1 analogs and potentially other peptide-based biopharmaceuticals.