RESUMO
We found that the extract of the body wall of the sea urchin, Pseudocentrotus depressus, agglutinate Escherichia coli and is inhibited by mannose. A mannose-binding protein of 22 kDa was purified via affinity chromatography using mannose-agarose. Amino acid sequences obtained by Edman degradation and liquid chromatography quadrupole time-of-flight mass spectrometry followed by de novo sequencing suggested that the protein is a C-type lectin. Products of PCR with a degenerate primer pair and of RACE PCR for the cDNA of the 22 kDa protein were sequenced and produced two full-length cDNA sequences encoding C-type lectins. These two lectins, named P. depressus mannose-binding C-type lectin (PdMBCL) 1 and 2 are composed of 187 and 189 amino acid residues, including signal peptides, respectively, and share 86% identity in their mature form. PdMBCLs agglutinated Lactococcus garvieae, a Gram-positive fish pathogen. Reverse transcription PCR showed that both the genes for the PdMBCLs were expressed in the body wall and in other tissues. Furthermore, the lectins were detected from a rinse of the body surface. Taken together, the present study showed that PdMBCLs function as anti-microbial agents on the body surface of P. depressus.