CHAPTER 56 Insect Venom Peptides MARIO SERGIO PALMA ABSTRACT to the extraordinary diversity of their chemical defense mechanisms [51]. In addition to the glandular defensive The insects of the order Hymenoptera (bees, wasps, secretions, some arthropods developed sophisticated and ants) are classified in two groups, based on their offensive/defensive chemical weaponry. In this regard, life history: social and solitary. The venoms of the social the development of venoms and its injection apparatus Hymenoptera evolved to be used as defensive tools to among the Insecta represented evolutionary attributes protect the colonies of these insects from the attacks of that contributed to adaptation of the insects to the many predators. Generally they do not cause lethal effects different terrestrial environments [51]. Thus, different but cause mainly inflammatory and/or immunological orders of the Insecta developed their self-chemical reactions in the victims of their stings. However, some- weaponry, particularly the Hymenoptera (bees, wasps, times it is also possible to observe the occurrence of and ants) that evolved into their venoms and stinging systemic effects like respiratory and/or kidney failure. apparatuses according to their biology and behavior. Meanwhile, the venoms of solitary Hymenoptera evolved The species with a solitary life history evolved their mainly to cause paralysis of the preys in order to permit venoms to be used as paralytic tools in order to keep egg laying on/within the prey’s body; thus, some com- their prey alive for feeding and reproduction. The many ponents of these venoms cause permanent/transient wasp species taking this evolutionary way include the paralysis in the preys, while other components seem to solitary aculeate wasps belonging to the superfamilies act preventing infections of the food and future prog- Bethyloidea, Scolioidea, Pompiloidea, Sphecoidea, and enies. The peptide components of venoms from Hyme- Vespoidea. This last superfamily is considered as a noptera are spread over the molar mass range of 1400 single family, the Vespinae, and contains the solitary to 7000 Da and together comprise up to 70% of the families Massarinae and Eumeninae as well as the social weight of freeze-dried venoms. Most of these toxins are Vespinae [37]. Members of this group of solitary wasps linear polycationic amphipatic peptides with a high are seasonal, spending the cooler periods as diapausing content of a-helices in their secondary structures. These larvae in nests provided by the mother-wasp. In the most peptides generally account for cell lysis, hemolysis, anti- cases, the food provided consists of arthropod prey biosis, and sometimes promote the delivery of cellular paralyzed by injection of venom into their bodies. The activators/mediators through interaction with the G- immobilized prey is then carried to the nest, where the protein receptor, and perhaps some of them are even eggs are layed on the prey and the larval development immunogenic components. In addition to these takes place [37]. The constituents of these venoms are peptides, the Hymenopteran venoms also may contain low-molecular-mass neurotoxins, such as polyamines, a few neurotoxins that target Na+ and/or Ca+2 channels a cocktail of neurotransmitters, and a few peptides [26], or even the nicotinic ACh receptor. This review sum- which are discussed later in this chapter. Another marizes current knowledge of the biologically active group of solitary wasps, the Terebrant, which include Hymenoptera venoms. the superfamilies Ichneumoidea, Cynipoidea, and Chalcicoidea evolved in the direction of parasitic INTRODUCTION behavior—that is, their venom evolved to promote short/ long-lasting transient paralysis of the prey in order to The remarkable dominance of insects and other permit egg-laying on/within the prey’s body. In this case, arthropods on land can be attributed, at least partially, after the egg laying, the prey recovers from the paralysis K2 The Handbook of Biologically Active Peptides 409 Copyright © 2006 Abba J. Kastin Ch056-P369442.indd 409 2/17/06 2:33:31 PM 410 / Chapter 56 and carries the eggs of the parasitic wasps [37]. In this noptera venoms and the references mentioned will situation, the venom of these solitary wasps evolved to enable a more extensive search of the literature. cause prey paralysis and seem to be constituted of high- molecular-mass proteins and low-molecular-mass com- pounds, generally presenting neurotoxicity. No peptide PEPTIDES FROM THE VENOMS component is presently known for these venoms so that OF SOCIAL HYMENOPTERA no further discussion about these components will be considered in the present chapter. The peptide components of venoms from social Meanwhile, those species that evolved in the Hymenoptera are spread over the molar mass range of direction of social behavior developed the formation 1400 to 7000 kDa and together comprise up to 70% of of castes and established the hierarchic relationship the weight of freeze-dried Hymenoptera venoms [36]. among nestmates of different castes. Generally the Most of these peptides have polycationic amphipatic social species built large nests containing many workers components, presenting a high content of a-helices in and larvae, in addition to storage of a reasonable their secondary structures; these peptides generally amount of pollen, honey, or nectar dew, attracting many account for cell lysis, hemolysis, antibiosis, and some- different types of predators to their nests [45]. These times promote the delivery of cellular activators/medi- species evolved their venom to prevent the presence of ators. In addition to this, the Hymenopteran venoms predators, keeping them far from the colonies; the also may contain a few neurotoxic peptides. venom of these species is not used to promote lethal actions but to produce mneumonical actions on the Peptide Toxins from Honeybee Venom victims of their stinging due to the uncomfortable effects of venoms such as pain, local burning, edema, Honeybee (Apis mellifera) venom contains well known swelling, bradycardia, tachycardia, headache, and, peptides such as: melittin, apamin, tertiapin, secapin, sometimes systemic effects like respiratory and/or and MCD-peptide. Some of these peptides present a kidney failure [32]. The venom of the social Hymenop- detergent-like action on plasma membranes [8], causing tera consist of complex mixture of proteins, peptides, cell lysis, while others are neurotoxins. Some aspects of and low molecular mass compounds. The enzymes are the primary sequences, secondary structures and the responsible for the injury caused to tissues and fre- biological actions will be emphasized. quently are immunogenic and therefore related to the allergy caused by these venoms in the victims of wasp Melittin and/or bee stings [13, 53]. Most abundant components of the venoms from social wasps and bees consist of Melittin is the major component of honeybee venom, peptide toxins. representing about 50% of the total honeybee venom. Ants contain some groups of species that may be It consists of 26 amino acid residues, mostly with hydro- considered as the most specialized among the social phobic or at least uncharged side chains, except for the insects, as well as contain species that may be consid- C-terminal region. Melittin can aggregates into a tetra- ered as the least specialized ones. Some species form meric form into the venom reservoir, being apparently small and secretive cryptic colonies, preying only on a inactive under this condition [4]. This peptide lowers limited group of organisms, while other species live the surface tension of water at the level of the plasma almost anywhere [5]. The ant venoms may be broadly membrane, acting mainly by its natural detergent-like classified as either predominantly consisting of protein effect on the plasma membrane, causing cell lysis (spe- and peptides or as a complex mixture of low-molecular- cially of mast cells), followed by histamine delivery. Due mass compounds. The ant species from the subfamilies to this lytic effect on cell membranes, this peptide may Ponerinae, Myrmiciinae, Pseudomyrmecinae, and be considered as a venom diffusion factor, facilitating Ecitoninae generally contain venom rich in proteins the entry of venom into the blood stream of the stung and peptides. victims. X-ray crystallography of mellitin indicated that This chapter summarizes the current knowledge the residues 1 to 10 and residues 13 to 26 form a-helixes concerning the biochemical and pharmacological prop- aligned about 120° to each other, while the proline in erties of the most representative peptide toxins from position 14 was suggested to be the cause of a bend in insects of the order Hymenoptera, which are now thor- the middle of the rod structure [11]. Thus, a single oughly characterized. It is not easy to comprehensively polypeptide chain has the conformation of a bent review the extensive literature on all the major compo- alpha-helical cylinder [8]. When packed, the tetramer nents of these venoms in the available space. Therefore, does so in a double planar layer. In order to achieve for the interest of readers the focus will be on the most tight hydrophobic interactions, the hydrophobic resi- K2 relevant groups of biologically peptides from Hyme- dues of all four chains extend toward the center of the Ch056-P369442.indd 410 2/17/06 2:33:31 PM Insect Venom Peptides / 411 tetramer. Due to its surfactant properties melittin is It produces cytolysis, thus being considered a potent considered a direct hemolytic factor, acting synergisti- mast cell degranulator, causing the release of histamine cally with phospholipase A2, activating this enzyme [4]. This peptide is a facilitator of the response of hon- [4]. eybee venom, responsible for the reddening, swelling, and locally occurring pain at the site of honeybee sting- ing, typical of histamine-mediated responses. Apamin The honey bee venom also contains apamin, a Other Peptides peptide of 18 amino acid residues. The CD spectros- copy study of apamin in solution is consistent with a Secapin represents about 0.5% of total honey bee peptide presenting as an alpha-helix an demonstrating venom.