1997 Volume 121 Issue 6 Pages 1002-1009
Some properties of recombinant proteins derived from the 32-kDa galectin isolated from the nematode Caenorhabditis elegans, which lectin is composed of two tandemly repeated homologous domains [Hirabayashi et al. (1992) J. Biol. Chem. 267, 15485], were studied in order to elucidate the function of this unique polypeptide architecture. We expressed the whole molecule (N32), the N-terminal lectin domain (Nh), and the C-terminal lectin domain (Ch) in Escherichia coli using the expression vector pET21a. All of the recombinant proteins were bound by asialofetuin-Sepharose. CD spectra of the recombinant proteins indicated all of them to be rich in β-structure and properly refolded. Gel filtration on an HPLC column suggested that all of them existed as monomers. Neither Nh nor Ch seemed to form dimers, in contrast to vertebrate proto-type galectins. Only N32 showed hemagglu-tination activity towards trypsinized rabbit erythrocytes. Comparison of the affinity of N32, Nh, and Ch for asialofetuin-Sepharose by frontal affinity chromatography [Kasai et al. (1986) J. Chromatogr. 376, 33] showed that Ch has 7-fold weaker affinity than N32, and Nh proved to have still weaker affinity. Since the Asn residue in the CRD (carbohydrate recognition domain), which is conserved in all other galectins, is substituted by Ser in the case of Nh, these data suggest that the two CRDs in this tandem-repeat galectin have different sugar binding properties and that the 32-kDa galectin may serve as a heterobifunc-tional crosslinker.
