Ice affinity purification system for recombinant proteins using a DUF3494 ice-binding protein.

Protein purification is essential for the isolation of specific proteins from mixtures. Conventional affinity tags have advanced recombinant protein purification. However, their reliance on costly resins and complex procedures often limits scalability and affordability. In this study, we identified three ice-binding domains (CoIBD1, CoIBD2, and CoIBD3) in Candidatus Cryosericum odellii SMC5 to evaluate their potential as protein purification tags. These domains exhibited hyperactive ice-binding properties, including high thermal hysteresis and ice recrystallization inhibition activities; additionally, they bound to multiple ice planes, enabling efficient attachment to ice surfaces. Through sequence and structural analyses, we engineered an enhanced variant that retained these ice-binding traits while achieving improved thermal and chemical stability: eCoIBD1. We then used eCoIBD1 as a fusion tag to develop the Ice Affinity Purification (IAP) system and evaluated its performance with GFP as a model protein. The IAP system achieved 87 % purity after two purification rounds, recovering 29 % of the initial protein from the crude extract. Consistent performance was observed in the presence of additives such as dithiothreitol and glycerol. The IAP system provides a cost-effective, environmentally friendly alternative to traditional methods by leveraging ice as a renewable binding medium, thereby eliminating the need for expensive resins or regeneration steps.