Preparation of Recombinant Galectin-3 for Cancer Studies

Galectin-3 is a member of a class of proteins termed Galectins, characterized by their ability to bind glycans containing β-galactose (Cummings and Liu, 2009). Galectin-3 binds preferentially to proteoglycans terminating with N-acetyllactosamine (LacNAc) chains (i.e., tandem repeats of galactose) (Newlaczyl and Yu, 2011). Galectin-3 is unique among the galectins in its chimeric structure. It shares a conserved carbohydrate recognition domain (CRD) with the other galectins, but has a long amino-terminal tail that is thought to be involved in protein aggregation. It can also form homodimers through its CRD (Cummings and Liu, 2009). Galectin-3 has been found to have diverse functions in tumorigenesis including: signaling, apoptosis inhibition, immune suppression, cell growth, and metastasis among others. Galectin-3 is frequently upregulated in cancers (Nangia-Makker et al., 2008). Its function largely depends on its expression and localization properties (Newlaczyl and Yu, 2011). Because of its many roles in cancer-associated processes, establishing a method for Galectin-3 production is valuable for further study of its functions in cancer. Here, we describe how Galectin-3 purification was achieved by cloning of the human Galectin-3 gene into pGEX-2T vector containing the gene for glutathione-S-transferase (GST) upstream of its cloning site. The Galectin-3 gene was cloned into this vector via restriction digests of both the plasmid and the Galectin-3 gene by restriction enzymes BamHI and EcoRI, followed by ligation of the two fragments. The resulting plasmid was then used to transform BL21, an Escherichia coli (E. coli) strain specialized for protein expression. Finally, we discuss how the GST fusion protein was isolated and the recombinant Galectin-3 protein was further purified from the GST.