Characterization of highly concentrated serum lectins in spotted halibut Verasper variegatus

Mannose-binding lectins were purified from flatfish spotted halibut (Verasper variegatus) serum. These lectins, which we named VVL (Verasper variegatus lectin)-alpha (approximately 33 kDa) and VVL-beta (approximately 30 kDa) (VVLs), under non-reducing SDS-PAGE, were surprisingly highly concentrated in serum (1.92+/-0.55 mg/ml; n=5), compared with other serum lectins. Both VVLs are heterodimers comprised of 2 types of subunit via inter-subunit disulfide bonds, and one subunit of VVL-alpha has a N-linked sugar chain. Based on N-terminal amino acid sequences, the nucleotide sequences of one subunit of VVL cDNAs were determined by 3'- and 5'-rapid amplification of the cDNA ends. The full-length VVL subunit cDNAs contained 489 bp, encoding an open reading frame of 163 amino acids. We found that VVLs bind to an approximately 8 kDa ciliary surface glycoprotein (a putative agglutination/immobilization antigen that we reported previously) of the fish parasite Neobenedenia girellae, and agglutinate this parasite in vitro.