Scalable production of functional recombinant human plasma gelsolin in Escherichia coli for therapeutic and diagnostic applications.

Human plasma gelsolin (pGSN) is an 83 kDa actin-binding protein involved in cytoskeletal remodeling, inflammation, and host defense. Its clinical relevance as a biomarker and potential therapeutic agent, particularly in conditions like sepsis, acute respiratory distress syndrome (ARDS), and cystic fibrosis, has driven interest in scalable recombinant expression. However, high-yield production of functionally active gelsolin is hindered by its complex structure and folding requirements. To address this, we developed a scalable, high-yield bacterial expression system that achieves among the highest reported levels of functional recombinant human gelsolin (rGelsolin) using a GST-fusion strategy incorporating a tobacco etch virus (TEV) protease cleavage site, optimized for solubility and downstream processing. High-density fed-batch fermentation in E. coli yielded 5.0 g/L of soluble protein. Following a three-step purification process with removal of the GST tag, 2.1 g/L of tag-free, high-purity rGelsolin with >95 % purity was obtained. Structural characterization by circular dichroism spectroscopy confirmed that rGelsolin adopted a native-like secondary structure and exhibited thermal stability (Tm ∼59 °C). Correct processing of the recombinant protein was verified by N- and C-terminal sequencing. Functional assays demonstrated that rGelsolin bound to and severed actin filaments in a calcium-dependent manner, similar to native plasma gelsolin. These findings demonstrate a scalable, cost-effective platform for producing bioactive rGelsolin in E. coli, with structural and functional features comparable to native pGSN, supporting its potential utility in diagnostic, therapeutic, and structural applications in the context of acute and chronic inflammatory diseases.