cDNA cloning and characterization of an antimicrobial peptide from Lumbricus rubellus

Abstract

A potent and structurally novel antimicrobial peptide was isolated and characterized from Lumbricus rubellus, an earthworm. The 62-amino acid peptide, named lumbricin, was purified by a heparin-affinity column and reversed phase HPLC. A cDNA clone for lumbricin was isolated from L. rubellus cDNA library. DNA sequence analysis revealed that the cloned cDNA was 555 base pairs in length and contained an open reading frame of 231 base pairs. The lumbricin precursor consisted of 76 amino acids, with 14 residues in a pre-segment, and the mature lumbricin was rich in proline (15% in molar ratio). The high content of proline suggests that lumbricin has a rather random structure instead of an amphiphilic alpha-helical conformation responsible for the antimicrobial activity of other antimicrobial peptides such as magainin and buforin. Southern blot analysis showed that the lumbricin gene existed as a multi-copy gene. Northern blot analysis on total RNA revealed that the expression of lumbricin gene was developmentally controlled and was not induced by bacterial infection.