Agents that increase the permeability of the outer membrane.

CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 FIVE CHEMICALLY DIFFERENT GROUPS OF PEPTIDE ANTIBIOTICS . . . . . . . . . . .. 63 Linear, Mostly Helical, Peptides Without Cys, With or Without a Hinge . . . . . . . . . . . . . . . 63 Linear Pep tides Without Cys and with a High Proportion of Certain Residues . . . . . . . . . 67 Antibacterial Peptides with One Disulfide Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Peptides with Two or More S-S Bonds Giving Mainly or Only fJ-Sheet Structures. . . . . . . 69 Antibacterial Peptides Derivedfrom Larger Polypeptides with Other Known Functions . . 72 ANTIBACTERIAL PROTEINS AND ACTIVE FRAGMENTS OF SUCH PROTEINS . . . . 73

Peptide antibiotics and their role in innate immunity.

▪ Abstract Infection in insects stimulates a complex defensive response. Recognition of pathogens may be accomplished by plasma or hemocyte proteins that bind specifically to bacterial or fungal polysaccharides. Several morphologically distinct hemocyte cell types cooperate in the immune response. Hemocytes attach to invading organisms and then isolate them by phagocytosis, by trapping them in hemocyte aggregates called nodules, or by forming an organized multicellular capsule around large parasites. These responses are often accompanied by proteolytic activation of the phenoloxidase zymogen that is present in the hemolymph. A component of insect immune responses to bacteria is the synthesis by fat body and hemocytes of a variety of antibacterial proteins and peptides, which are secreted into the hemolymph. These molecules attack bacteria by several mechanisms. Inducible antifungal proteins have also been recently discovered in insect hemolymph. The promoters for several antibacterial protein genes in ins...

Biological mediators of insect immunity

Antimicrobial peptides appear to be ubiquitous and multipotent components of the innate immune defense arsenal used by both prokaryotic and eukaryotic organisms. During the past 15 years a multitude of these peptides have been isolated largely from insects. In spite of great differences in size, amino acid composition and structure, most of the antimicrobial peptides from insects can be grouped into one of three categories. The largest category in number contains peptides with intramolecular disulfide bonds forming hairpin-like β-sheets or α-helical–β-sheet mixed structures. The second most important group is composed of peptides forming amphipathic α-helices. The third group comprises peptides with an overrepresentation in proline and/or glycine residues. In general, the insect antimicrobial peptides have a broad range of activity and are not cytotoxic. Despite a wealth of information on structural requirements for their antimicrobial activity, the mode of action of these peptides is not yet fully understood. However, some data suggest the existence of two types of mode of action: 1. through peptide–lipid interaction or 2. through receptor-mediated recognition processes. This review presents the main results obtained during the last four years in the field of antimicrobial peptides from insects with a special focus on the proline-rich and cysteine-rich peptides.

Antimicrobial peptides in insects; structure and function

Antibiotic peptides are a key component of the innate immune systems of most multicellular organisms. Despite broad divergences in sequence and taxonomy, most antibiotic peptides share a common mechanism of action, i.e., membrane permeabilization of the pathogen. This review provides a general introduction to the subject, with emphasis on aspects such as structural types, post-translational modifications, mode of action or mechanisms of resistance. Some of these questions are treated in depth in other reviews in this issue. The review also discusses the role of antimicrobial peptides in nature, including several pathological conditions, as well as recent accounts of their application at the preclinical level.

Animal antimicrobial peptides: an overview.

Although insects lack the basic entities of the vertebrate immune system, such as lymphocytes and immunoglobulins, they have developed alternative defence mechanisms against infections. Different types of peptide factors, exhibiting bactericidal activity, have been detected in some insect species. These humoral factors are induced upon infection. The present report describes the discovery of the apidaecins, isolated from lymph fluid of the honeybee (Apis mellifera). The apidaecins represent a new family of inducible peptide antibiotics with the following basic structure: GNNRP(V/I)YIPQPRPPHPR(L/I). These heat-stable, non-helical peptides are active against a wide range of plant-associated bacteria and some human pathogens, through a bacteriostatic rather than a lytic process. Chemically synthesized apidaecins display the same bactericidal activity as their natural counterparts. While only active antibacterial peptides are detectable in adult honeybee lymph, bee larvae contain considerable amounts of inactive precursor molecules.

Apidaecins: antibacterial peptides from honeybees.

Honeybee (Apis mellifera) are frequently exposed to and likely to be infected by plant-associated bacteria. We mimicked this process by injecting bees with live bacteria and isolated five induced antibacterial substances by comparative liquid chromatographic mapping of the hemolymph. Three of these antibiotics belong to a unique family of small (18 amino acids) peptides: the apidaecins [Casteels et al. (1989) EMBO J. 8, 2387-2391]. We have now characterized a fourth bee immune response peptide. The complete sequence was established by Edman degradation of the peptide and fragments thereof. It is 34 amino acids long and contains 10 proline residues. The amino-terminal half is related to the apidaecins; similar proline motifs are also present in the amino-terminal quarter of the much longer fly diptericins. The newly identified peptide's broad spectrum, lower specific activities against Gram-negative plant pathogens and its inability to inhibit bacterial growth at medium ionic strength are different from the apidaecins. Moreover, the highest observed specific activity was against an apidaecin-resistant Xanthomonas strain. In contrast to the immediate action of apidaecins, bactericidal activity is delayed. We propose the name 'abaecin' for this new antibacterial response peptide.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1990.tb15315.x

Isolation and characterization of abaecin, a major antibacterial response peptide in the honeybee (Apis mellifera).

The 25 albumins, or napin-like proteins, constitute a significant portion of total seed protein in a variety of dicotyledonous species (Youle and Huang, 1981). In mature seed they are found as heterodimers, consisting of two subunits linked by disulfide bridges. They are synthesized as precursors that undergo posttranslational proteolytic processing (Crouch et al., 1983). In most species, they are encoded by multigene families (Josefsson et al., 1987; Scofield and Crouch, 1987; Raynal et al., 1991). Krebbers et al. (1988) reported the isolation and sequencing of an Arabidopsis 25 albumin isoform and used the sequence to isolate four genes that encode different isoforms. Hybridization studies suggested that this represented the entire gene family. In the course of experiments to separate individual 2 s albumin isoforms, we have now isolated a previously unknown isoform that is not encoded by any of the known genes.

/pdf/a-fifth-2s-albumin-isoform-is-present-in-arabidopsis-1h5kaxujdv.pdf

A Fifth 2S Albumin Isoform Is Present in Arabidopsis thaliana

The invention relates to new bactericidal and/or bacte­riostatic thermostable peptides which are isolatable from hemolymph of immune honeybees and which are distinct from lysozymes, attacins, cecropins, diptericins ans magainins. They have bactericidal or bacteriostatic properties or both. They are useful in the field of therapy and prophilaxy in man or animal, in the field of plant pathogen control or in the field of food and feed control.

Bactericidal and/or bacteriostatic peptides, process for their isolation, their production and their applications

New bactericidal and/or bacteriostatic, thermostable peptides which are isolated from hemolymph of immune honeybees and which are distinct from lysozymes, attacins, cecropins, diptericins and magainins. The peptides feature at least the 10 C-terminal amino acids of the following peptide: H2 N-Gly-Asn-Asn-Arg-Pro-X-Tyr-Ile-Pro-Gln-Pro-Arg-Pro-Pro-His-Pro-Arg-Z-OH in which X is a valyl or isoleucyl residue and Z is a leucyl or isoleucyl residue.

Bactericidal and/or bacteriostatic peptides isolated from hemolymph of honeybees

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