Amino acid sequence of a lectin from the sea cucumber, Stichopus japonicus, and its structural relationship to the C-type animal lectin family.

The complete amino acid sequence of SJL-I, a lectin from the sea cucumber, Stichopus japonicus, was determined by sequence analysis of peptides derived on enzymatic and chemical fragmentation of the protein. SJL-I consists of 143 amino acid residues and its molecular mass was calculated to be 15,837 Da. Comparison of the sequence of SJL-I with a database revealed that SJL-I exhibits apparent homology with C-type lectins, especially with those of marine invertebrates. The highest homology (identity 28.6%) was found with echinoidin, a lectin from the sea urchin, Anthocidaris crassispina. Comparison of the sequence of SJL-I with those of other C-type lectins indicated that the conserved amino acids are relatively abundant in the C-terminal half of their carbohydrate-recognition domains (CRDs), that can be considered to be involved in binding with Ca2+ as well as carbohydrates.