Insect immunity

Abstract

Injury or injection of live bacteria into third instar larvae of the dipteran insect Phormia terranovae results in the appearance in the haemolymph of at least five groups of heat-stable, more or less basic peptides with antibacterial activity against Escherichia coli. Three of these peptides have been purified. The amino acid sequence has been completely established for one of these and partially (first 40 residues from the N-terminus) for the two others. The sequences show marked homologies indicating that the three peptides belong to a common family. They are not related to other known antibacterial peptides from insects [lysozymes, cecropins (including sarcotoxin I) and attacins]. We propose the name of diptericins for this new family of antibiotic molecules.It is now well established that lepidopteran and dipteran insects respond to a bacterial challenge and also to injury by synthesizing peptides with antibacterial activity (reviewed in Boman and Gotz [l]). Several antibacterial molecules induced in Hyalophora cecropia have been fully or partially characterized : these are the cecropins (3 -5 kDa basic, heatstable peptides) [2], the attacins (20 kDa basic or acidic proteins) [3] and lysozymes [4]. In dipterans, only one induced antibacterial protein has been characterized so far; it is a basic 39-residue molecule named sarcotoxin I, isolated from the blood of injured flesh-fly larvae Sarcophaga peregrina; this molecule shares significant homology with cecropins and is found in at least three forms [5].In the course of an investigation into the cellular and humoral defence reactions of the dipteran Phormia terranovae, a species closely related to Calliphora erythrocephala, we have recently obtained evidence for the appearance in the haemolymph of immunized larvae of a number of heat-stable, basic antibacterial proteins [6, 71. There are at least five of these proteins (or groups of proteins) in the immune haemolymph; none of them corresponds to lysozyme.In the present paper we show that three of these proteins belong to a novel class of antibacterial peptides; in particular, they differ from cecropins, attacins and lysozymes. We propose that they should be named diptericins. We report how, starting with immune plasma of Phormia, we have isolated the induced protein which shows the highest antibacterial activity on Escherichia coli in our assay conditions. It is a basic molecule (PI = 8.5) containing 82 amino acid residues with a relative molecular mass of 8610. We have determined the complete amino acid sequence of this major form (diptericin A) and sufficient N-terminal sequence of two of the minor forms (diptericins B and C) to reveal that there is a family of diptericins of related structure.

Complete amino acid sequence of the neurone‐specific γ isozyme of enolase (NSE) from human brain and comparison with the non‐neuronal α form (NNE)

“…In general, the difference between the two sequencing methods is that cDNA work involves the cloning of a single copy of the nucleotide sequence whereas amino acid sequencing usually involves a large number of molecules produced in different cells, frequently in different tissues, and sometimes in different individuals all of whom can theoretically be heterozygous at any position in the sequence. This difference in starting material can lead, on the one hand, to anomalies in cDNA sequence, as for example in irregular intron excision [7, 181, or on the other can show substantial heterogeneities in amino acid sequence when proteins are purified from a large number of individuals [19]. In this case we have no reason to doubt the evidence that alanine occurs at position 394 in some molecules of y enolase, and that there may be a small percentage of molecules with an alanine residue at position 264.…”

Antimicrobial peptide defense in Drosophila

“…Proline-rich antibacterial peptides are also present in bovine n e u t r~p h i l e s (~~) and in pig intestine (42), although sequence homology with the insect peptides does not appear to exist. (4) Glycine-rich polypeptides These form a heterogeneous family of immune-inducible insect polypeptides, with sizes ranging from 8 to 30 kDa (43,44), which have in common a higher-than-average proportion of glycine residues (10-21%) (11). They are mainly active against Gram-negative germs.…”

Magainin Oligomers Reversibly Dissipate .DELTA..mu.H+ in Cytochrome Oxidase Liposomes

“…Synthetic analogues of these magainins have been shown to be even more active in antimicrobial assays than the parent compounds JuretiC et al, 1989). Magainins may be part of a structurally heterogeneous, but functionally definable, class of oligopeptides (Boman & Hultmark, 1987;Dimarcq et al, 1988;Lehrer et al, 1988;Nakajima et al, 1987; Bevins & Zasloff, 1990; Boman, 199 1) that provide a secondary immune system for organisms as diverse as insects, amphibia, and man.At pH 7, magainins are positively charged, amphiphilic oligopeptides consisting of some 23 amino acids (Zasloff, 1987; f This study was supported by the Netherlands Organization for Scientific Research (NWO). …”