Color-coded galectin fusion proteins as novel tools in biomaterial science

The inherent carbohydrate-binding specificities of human galectins can serve as recognition elements in both biotechnological and biomedical applications. The combination of the carbohydrate-recognition domain (CRD) of galectins fused to peptides or proteins for purification, immobilization, and imaging enables multifunctional utilization within a single protein. We present here a library of color-coded galectin fusion proteins that incorporate a His6-tag, a fluorescent protein, and a SpyCatcher or SpyTag unit to enable immobilization procedures. These galectin fusion proteins exhibit similar binding properties to the non-fused galectins with micromolar apparent binding affinities. N- and C-terminal fusion partners do not interfere with the SpyCatcher/SpyTag immobilization. By applying SpyCatcher/SpyTag-mediated SC-ST-Gal-3 conjugates, we show the stepwise formation of a three-layer ECM-like structure in vitro. Additionally, we demonstrate the SpyCatcher/SpyTag-mediated immobilization of galectins in microgels, which can serve as a transport platform for localized targeting applications. The proof of concept is provided by the galectin-mediated binding of microgels to colorectal cancer cells.