Attacins: A Promising Class of Insect Antimicrobial Peptides

Abstract

Insects produce a large repertoire of antimicrobial peptides (AMPs) as the first line of defense against bacteria, viruses, fungi or parasites. These peptides are produced from a large precursor that contains a signal domain, which is cleaved in vivo to produce the mature protein with antimicrobial activity. At present, AMPs from insects include several families which can be classified as cecropins, ponericins, defensins, lebocins, drosocin, Metchnikowin, gloverins, diptericins and attacins according to their structure and/or function. This short review is focused on attacins, a class of glycine-rich peptides/proteins that have been first discovered in the cecropia moth (Hyalophora cecropia). They are a rather heterogeneous group of immunity-related proteins that exhibit an antimicrobial effect mainly against Gram-negative bacteria. Here, we discuss different attacin and attacin-like AMPs that have been discovered so far and analyze their structure and phylogeny. Special focus is given to the physiological importance and mechanism of action of attacins against microbial pathogens together with their potential pharmacological applications, emphasizing their roles as antimicrobials.

Keywords: antimicrobial activity; attacins; insect AMPs; pharmacological applications.

Figure 1

Alignment of attacin amino acid sequences from Lepidoptera obtained by Clustal ω. The predicted signal peptide and the different domains are highlighted above the sequences, together with the RXXR motif (indicated as cut symbol). Accession numbers: Trichoplusia ni U46130; Hyphantria cunea Attacin B ABL63641; Danaus plexippus plexippus OWR54405; Hyphantria cunea Attacin A AAD09288; Manduca sexta AAY82587; Bombyx mori 2 Q26431; Bombyx mandarina XP_028041931; Bombyx mori 1 ADB08384; Hyalophora cecropia Basic CAA44179; Samia ricini BAB69462; Lonomia obliqua Q5MGE6; Hyalophora cecropia Acidic CAA40886; Antheraea mylitta ABG72695; Antheraea pernyi ACB45562; Antheraea yamamai AFS30776. Sequence conservation is shown as a histogram below the multiple sequence alignment; Att = Attacin.

Figure 2

Phylogenetic tree of attacins from different insect orders obtained using the MEGA 6.0 program. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (10.000 replicates) is shown next to the branches. The number 0.2 represents the genetic distance. Accession numbers: Drosophila simulans Attacin A EDX07123; Drosophila yakuba EDW91058; Drosophila melanogaster Attacin A Z46893; Drosophila obscura XP_022225780; Drosophila busckii ALC41796; Drosophila melanogaster Attacin B AAL23652; Drosophila simulans Attacin C AAP69835; Ceratitis capitata Attacin A XP004517761; Ceratitis capitata Attacin C XP004517762; Bactrocera dorsalis KJ598077; Musca domestica AAU08203; Glossina morsitans morsitans Attacin A AAL34113; Glossina morsitans morsitans Attacin D CAP78962; Lucilia sericata HM243534; Drosophila melanogaster Attacin D AAF55446; Drosophila yakuba Attacin D EDW95807; Microdera dzhungarica AHH34162; Anatolica polita APX53001; Diabrotica virgifera virgifera AHB11276; Onthophagus taurus XP_022912795; Leptinotarsa decemlineata XP_023024624. For the Lepidoptera accession numbers, see Figure 1. Att = Attacin.