Purification, characterization, and amino acid sequence of an embryonic lectin in perivitelline fluid of the horseshoe crab

Hemagglutinating activity in perivitelline fluid of the horseshoe crab embryo dramatically increases during the third and fourth molt of the embryo. A 27-kDa lectin, which we named tachylectin-P (TL-P), was newly identified in perivitelline fluid of the horseshoe crab Tachypleus tridentatus. TL-P preferentially agglutinated human A-type erythrocytes, and the activity was inhibited by N-acetyl group-containing monosaccharides. The amino acid sequence analysis indicated that TL-P is almost structurally the same as a hemocyte-derived lectin with no hemagglutinating activity, tachylectin-1 (TL- 1), and that 218 out of 221 amino acid residues in total were conserved between the two lectins. Despite the high sequence similarity, biological and biochemical characteristics of TL-P differed from those of TL-1: (i) unlike TL-1, TL-P agglutinates several animal-derived erythrocytes; (ii) unlike TL- 1, TL-P has no significant affinity for bacterial lipopolysaccharides or antibacterial activity; (iii) Based on apparent molecular masses determined by gel filtration, TL-P forms a dimer in solution, while TL-1 is present as a monomer; (iv) and TL-P interacts with endogenous proteins of 13 and 14 kDa present in the perivitelline fluid; however, neither has any affinity for TL- 1. We propose that TL-P may have an important role in completing embryonic development by interacting with endogenous glycoproteins or N- acetylhexosamines.