LUMBRICIN-I, A NOVEL PROLINE-RICH ANTIMICROBIAL PEPTIDE FROM THE EARTHWORM - PURIFICATION, CDNA CLONING AND MOLECULAR CHARACTERIZATION

A novel antimicrobial peptide was isolated and characterized from the earthworm, Lumbricus rubellus. The antimicrobial peptide was purified to homogeneity by a heparin-affinity column and C18 reverse-phase HPLC , and named lumbricin I. Lumbricin I was a proline-rich antimicrobial peptide of 62 amino acids (15% proline in molar ratio; molecular mass, 7231 Da), whose complete sequence was determined by a combination of peptide sequence and cDNA analysis. The peptide and cDNA sequence anal ysis revealed that lumbricin I was produced as a precursor form consis ting of 76 amino acids, with 14 residues in a presegment and 62 residu es in mature lumbricin I. Lumbricin I showed antimicrobial activity in vitro against a broad spectrum of microorganisms without hemolytic ac tivity. In addition, a 29-amino acid peptide, named lumbricin I(6-34), which was derived from residues 6-34 of lumbricin I, showed marginall y stronger antimicrobial activity than lumbricin I. Northern blot anal ysis on total RNA revealed that expression of lumbricin I gene was not induced by bacterial infection, but was constitutively expressed. Fur thermore, the expression of lumbricin I gene was specific in adult L. rubellus: Lumbricin I mRNA was detected only in adult L, rubellus, but not in eggs and young L. rubellus. (C) 1998 Elsevier Science B.V. All rights reserved.