Caenorhabditis elegans proteins captured by immobilized Galβ1-4Fuc disaccharide units: assignment of 3 annexins.

Galβ1-4Fuc is a key structural motif in Caenorhabditis elegans glycans and is responsible for interaction with C. elegans galectins. In animals of the clade Protostomia, this unit seems to have important roles in glycan-protein interactions and corresponds to the Galβ1-4GlcNAc unit in vertebrates. Therefore, we prepared an affinity adsorbent having immobilized Galβ1-4Fuc in order to capture carbohydrate-binding proteins of C. elegans, which interact with this disaccharide unit. Adsorbed C. elegans proteins were eluted with ethylenediaminetetraacetic acid (EDTA) and followed by lactose (Galβ1-4Glc), digested with trypsin, and were then subjected to proteomic analysis using LC-MS/MS. Three annexins, namely NEX-1, -2, and -3, were assigned in the EDTA-eluted fraction. Whereas, galectins, namely LEC-1, -2, -4, -6, -9, -10, and DC2.3a, were assigned in the lactose-eluted fraction. The affinity of annexins for Galβ1-4Fuc was further confirmed by adsorption of recombinant NEX-1, -2, and -3 proteins to the Galβ1-4Fuc column in the presence of Ca(2+). Furthermore, frontal affinity chromatography analysis using an immobilized NEX-1 column showed that NEX-1 has an affinity for Galβ1-4Fuc, but no affinity toward Galβ1-3Fuc and Galβ1-4GlcNAc. We would hypothesize that the recognition of the Galβ1-4Fuc disaccharide unit is involved in some biological processes in C. elegans and other species of the Protostomia clade.