Glycobiology Advance Access published online on September 21, 2007
Glycobiology, doi:10.1093/glycob/cwm093
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Molecular and Biological Characterization of a Mannan-Binding Lectin from the Holothurian Apostichopus Japonicus
1 Pacific Institute of Bioorganic Chemistry, Far Eastern Branch, Russian Academy of Science, Vladivostok, 690022, Russia
2 Institute of Marine Biology, Far Eastern Branch, Russian Academy of Science, Vladivostok 690041, Russia
3 To whom all correspondence including proofs and reprints should be addressed at: Pacific Institute of Bioorganic Chemistry, Far Eastern Branch, Russian Academy of Science, Vladivostok, 690022, Stoletya Vladivostoku str. 159, Russia. phone: +7 4234 310719, fax +7 4234 314050, e-mail: aabulgakov{at}yahoo.com
Received on January 15, 2007; revised on August 30, 2007; accepted on August 31, 2007
To elucidate the origin and evolution of mannan-binding lectins (MBL), a new C-type lectin specific for high-mannose glycans (MBL-AJ) was isolated from the coelomic plasma of the holothurian Apostichopus japonicus. MBL-AJ has oligomeric forms with identical 17-kDa subunits on SDS-PAGE. Among natural ligands, lectin hemagglutination activity was competitively inhibited by extracellular low-branched, but not high-branched,
-D-mannans isolated from marine halophilic bacteria and composed of
-1,2 and
-1,6 linked D-mannose residues. This suggests that lectin interacts with backbone or inner side chain mannose residues, but not with terminal ones. The activity of the lectin was Ca2+, pH, and temperature–dependent.
MBL-AJ cDNA was cloned from a holothurian coelomocyte cDNA library. The subunit of the mature protein has 159 amino acids and a single carbohydrate-recognition domain (CRD) of C-type lectin. CRD contains a Glu-Pro-Asp amino acid sequence (EPN-motif) conserved for all known mannan-binding lectins.
A monospecific polyclonal antibody against MBL-AJ was obtained using the 34-kDa lectin dimer as an immunogen. The MBL-AJ has demonstrated immunochemical identity to the earlier isolated mannan-binding C-type lectin from the other holothurian, Cucumaria japonica. But more interesting finding was cross-reactivity of MBL-AJ and human serum MBL detected by the antibody against MBL-AJ. Taking into consideration such MBL-AJ peculiarities as its carbohydrate specificity, the presence of conserved region forming the mannose-binding site, common antigenic determinants with human MBL, and participation in defense reactions, it is possible that MBL-AJ belongs to the family of evolutionary conservative mannan-binding proteins.
Key words: Apostichopus japonicus / bacterial mannans / Echinoderms immunity / mannan-binding lectins