Metchnikowin, a Novel Immune‐Inducible Proline‐Rich Peptide from Drosophila with Antibacterial and Antifungal Properties

Abstract

One of the characteristics of the host defense of higher insects is the rapid and transient synthesis of a variety of potent antimicrobial peptides. To date, several distinct inducible antimicrobial peptides or peptide families have been totally or partially characterized. We present here the isolation and characterization of a novel 26-residue proline-rich immune-inducible peptide from Drosophila. which exhibits both antibacterial (Gram-positive) and antifungal activities. Peptide sequencing and cDNA cloning indicate the presense of two isoforms in our Drosophiln OregonK strain, which differ by one residue (His compared to Arg) as a consequence of a single nucleotide change. The gene, which maps in position 52A1-2 on the right arm of the second chromosome, is expressed in the fat body after immune challenge. The novel peptide, which we propose to name metchnikowin, is a member of a family of proline-rich peptides, and we discuss the possible evolutionary relationships within this family.

Two distinct pathways can control expression of the gene encoding the Drosophila antimicrobial peptide metchnikowin

“…This ORF comprises a putative signal peptide and the 26 amino acid residue long mature metchnikowin (Figure 4(b)). No additional sequences were found in the transcribed region of the metchnikowin genomic clone in comparison to the cDNA clone (Levashina et al, 1995), indicating that the gene encoding metchnikowin is intron-less. The location of the cap site was determined by primer extension (data not shown).…”

“…We have previously shown that metchnikowin expression is induced upon immune challenge in Drosophila adults, and reaches a maximum level 14 hours after septic injury (Levashina et al, 1995). As stated in the Introduction, two pathways have been shown to participate in the regulation of the humoral immune response in Drosophila.…”

“…These results are consistent with our present knowledge of the functions of the antimicrobial peptides in Drosophila, since Tl controls expression of the antifungal peptide gene drosomycin, while imd appears to control, or to participate in the control of, the antibacterial peptides. Here, we have investigated the regulation of expression of the newly discovered peptide metchnikowin, which has both antibacterial and antifungal activity (Levashina et al, 1995). We report that the regulation of this peptide is unique compared to the other peptides, in that it appears to be regulated independently by the TOLL and the IMD pathways.…”

“…Five of these peptides, cecropins , diptericin (Wicker et al, 1990), drosocin , attacin (Asling et al, 1995) and insect defensin (Dimarcq et al, 1994), are selectively active against bacteria, whereas drosomycin, is solely active against fungi (Fehlbaum et al, 1994). The seventh and most recently discovered molecule, metchnikowin, is unique among the antimicrobial peptides of Drosophila in that it is active against both bacteria and fungi (Levashina et al, 1995).…”

Penaeidins, a New Family of Antimicrobial Peptides Isolated from the Shrimp Penaeus vannamei (Decapoda)

“…For the time being and for convenience, these antimicrobial peptides are tentatively classified into four distinct groups based on amino acid sequences, secondary structures, and functional similarities: (i) linear basic peptides forming amphipathic ␣-helices including the cecropins, the first antimicrobial peptide isolated from insect hemolymph (for review see Ref. 9); (ii) peptides with one to six intramolecular disulfide bridges including the arthropod defensins (10), antifungal peptides from Drosophila, drosomycin (11) and metchnikowin (12), thanatin from Podisus (13), tachyplesin, big defensin and tachycitin from limulus (14 -16), and other cysteine-rich antimicrobial peptides isolated from a scorpion (17) and from a bivalve mollusk (18,19); (iii) prolinerich peptides, among them the apidaecins and abaecins from Hymenoptera (20,21) and drosocin from Drosophila hemolymph (22); (iv) glycine-rich antimicrobial peptides or polypeptides (9 -30 kDa) such as the attacins (23), diptericin (24) and sarcotoxins (25). The mode of action, the broad activity, the molecular diversity, and the noncytotoxicity of all these circulating antimicrobial peptides make them very attractive as therapeutic agents for pharmaceutical or agricultural applications (26,27).…”