Biochemical and ligand binding properties of recombinant Xenopus laevis cortical granule lectin-1

Intelectins are putative innate immune lectins that are found throughout chordates. The first intelectin reported was Xenopus laevis cortical granule lectin-1 (XCGL-1 or XL-35). XCGL-1 is critical in fertilization membrane development in Xenopus. Here, we explored the biochemical properties of XCGL-1. The cysteines responsible for forming intermolecular disulfide bonds were identified. XCGL-1 adopted a four-lobed structure as observed by electron microscopy. The full-length XCGL-1 and the carbohydrate recognition domain (CRD) bind galactose-containing carbohydrates at nanomolar to micromolar affinities. Molecular modeling suggested that galactoside ligands coordinated the binding site calcium ion and interacted with residues around the groove made available by the non-conserved substitution compared to human intelectin-1. Folding conditions for production of recombinant XCGL-1 CRD were also investigated. Our results not only provide new biochemical insights into the function of XCGL-1, but may also provide foundation for further applications of XCGL-1 as glycobiology tools.