Protein purification, cDNA cloning and gene expression of attacin, an antibacterial protein, from eri-silkworm, Samia cynthia ricini

Attacin was isolated from immunized larval hemolymph of the wild silkmoth, Samia cynthia ricini. The antibacterial effect of the attacin was limited to some species of Gram-negative bacteria. Two cDNA clones encoding attacin A and B, respectively, were isolated by screening the cDNA library from immunized fat body. The two cDNAs encoded the same length of precursor protein with 233 amino acid residues. The 46-residue prepropeptides of the two attacins were identical to each other, but 4 out of 187 residues of the mature proteins were different in each other. The two attacins show 98% identity at the amino acid level, while 92% identity at the nucleotide level. Both of the mature proteins were highly homologous to cecropia basic attacin with identity of 96%. The attacin transcripts were detected at significant level in fat body, hemocytes and Malpighian tube after injection with peptidoglyean, but not in the midgut and the silkgland. The induction of attacin gene expression was elicited most effectively by peptidoglycan and UV-killed bacteria in the fat body. (C) 2002 Elsevier Science Ltd. All rights reserved.