CLONING AND EXPRESSION OF THE GENE OF HEMOCYTIN, AN INSECT HUMORAL LECTIN WHICH IS HOMOLOGOUS WITH THE MAMMALIAN VON-WILLEBRAND-FACTOR

Invertebrate lectins play an important role in a non-specific self-def ense mechanism, as invertebrates do not synthesize specific antibodies . We report the cloning of several overlapping cDNAs encoding the enti re silkworm (Bombyx mori) lectin, which we propose to call hemocytin. The sequence (10477 bp) encoded 3133 amino acids. The characteristic f eatures of the carbohydrate-recognition domain of C-type animal lectin were revealed at C-terminal sequence of hemocytin. When cDNA encoding this region was introduced into baculovirus vector, hemagglutinating activities were detected in the culture fluid of a recombinant virus-i nfected cells. These activities were inhibited by D-mannose, N-acetyl- D-galactosamine, and D-maltose which are haptenic saccharides of authe ntic hemocytin. Analysis of dot and Northern blot hybridization reveal ed that hemocytin gene was transcribed in hemocytes of the silkworm at larval-pupal metamorphosis and/or after the injection of Escherichia coli and lipopolysaccharide. After silkworm larvae were injected with C-terminal portion of hemocytin, aggregation of hemocytes was observed in the hemolymph. Hemocytin has significant homology with mammalian v on Willebrand factor which involves in platelet adhesion to subendothe lium. Also, hemocytin has a homologous region with coagulation factor V and VIII. These results suggest that hemocytin molecule is an adhesi ve protein and relates to hemostasis or encapsulation of foreign subst ances for self-defense.