Arthropod Assassins: Crawling Biochemists with Diverse Toxin Pharmacopeias
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Accepted Manuscript Arthropod assassins: crawling biochemists with diverse toxin pharmacopeias Volker Herzig PII: S0041-0101(18)31041-9 DOI: https://doi.org/10.1016/j.toxicon.2018.11.312 Reference: TOXCON 6038 To appear in: Toxicon Please cite this article as: Herzig, V., Arthropod assassins: crawling biochemists with diverse toxin pharmacopeias, Toxicon, https://doi.org/10.1016/j.toxicon.2018.11.312. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT 1 Editorial 2 Arthropod assassins: crawling biochemists with diverse toxin pharmacopeias 3 Volker Herzig 1 4 5 6 1 Institute for Molecular Bioscience, The University of Queensland, St. Lucia QLD 4072, 7 Australia 8 9 10 11 *Address correspondence to: Volker Herzig, Institute for Molecular Bioscience, The University 12 of Queensland, St. Lucia QLD 4072, Australia; Phone: +61 7 3346 2018, Fax: +61 7 3346 2101, 13 Email: [email protected] 14 15 16 17 MANUSCRIPT 18 19 20 21 22 23 24 25 26 ACCEPTED 1 ACCEPTED MANUSCRIPT 27 Abstract 28 The millions of extant arthropod species are testament to their evolutionary success that can at 29 least partially be attributed to venom usage, which evolved independently in at least 19 arthropod 30 lineages. While some arthropods primarily use venom for predation (e.g., spiders and centipedes) 31 or defense (e.g., bees and caterpillars), it can also have more specialised functions (e.g. in 32 parasitoid wasps to paralyse arthropods for their brood to feed on) or even a combination of 33 functions (e.g. the scorpion Parabuthus transvaalicus can deliver a prevenom for predator 34 deterrence and a venom for predation). Most arthropod venoms are complex cocktails of water, 35 salts, small bioactive molecules, peptides, enzymes and larger proteins, with peptides usually 36 comprising the majority of toxins. Some spider venoms have been reported to contain > 1,000 37 peptide toxins, which function as combinatorial libraries to provide an evolutionary advantage. 38 The astounding diversity of venomous arthropods multiplied by their enormous toxin arsenals 39 results in an almost infinite resource for novel bioactive molecules. The main challenge for 40 exploiting this resource is the small size of most arthropods, which can be a limitation for current 41 venom extraction techniques. Fortunately, recent decades have seen an incredible improvement in 42 transcriptomic and proteomic techniques that have provided increasing sensitivity while reducing 43 sample requirements. In turn, this has provided a much larger variety of arthropod venom 44 compounds for potential applications such as therapeutics, molecular probes for basic research, 45 bioinsecticides or anti-parasitic drugs. This special issue of Toxicon aims to cover the breadth of 46 arthropod venom research, including toxin evolution, pharmacology, toxin discovery and 47 characterisation, toxin structures, clinical aspects, and potential applications. 48 49 50 1. Diversity of arthropod venom systems 51 Invertebrates within the phylum Arthropoda that MANUSCRIPTare characterised by segmented bodies and 52 paired jointed appendages are classified into the four extant subphyla Chelicerata, Myriapoda, 53 Crustacea and Hexapoda. Arthropods have been extremely successful over the course of 54 evolution and it is estimated that they comprise nearly 85% of all extant animal species (Giribet 55 and Edgecombe, 2012). Their evolutionary success story can partially be attributed to the use of 56 venoms, which have independently developed in all extant arthropod subphyla. Based on their 57 independent evolutionary origin (even multiple times within some lineages), the venom delivery 58 systems in arthropods can be localised in very different body regions (Fig. 1); for example, they 59 can be combined with, or close to, mouth parts (dipterans, bugs, spiders, ticks), present as 60 modified legs (centipedes, remipedes), in the palpal pincers (pseudoscorpions), in the antennae 61 (coleopterans - Cerambycidae), at the distal end of the body (scorpions and hymenopterans) or as 62 toxic hairs covering parts of the body (lepidopteran larvae). 63 64 ACCEPTED 2 ACCEPTED MANUSCRIPT 65 MANUSCRIPT 66 67 Fig.1: Venomous representatives of the four arthropod subphyla with the red arrows and the 68 zoomed images indicating the anatomic location of the venom delivery system. Photographs 69 authored by Tobias Hauke (Germany; spider, scorpion), Kriton Kunz (Germany; 70 pseudoscorpion), Mario Sergio Palma (Brazil; wasp, ant), Gavin Rice (Australia; caterpillar), 71 Ivo Muniz (Brazil; beetle), Eivind A.B. Undheim (Australia; centipede, assassin bug), Ingo Wendt 72 (Germany; robberACCEPTED fly, pseudoscorpion chelae, centipede focipules), Björn von Reumont 73 (Germany; remipede). 74 75 76 Crustaceans are the least well-studied arthropods in terms of venoms and only a single example 77 of a venomous crustacean, the cave-dwelling remipede Xibalbanus tulumensis , has been reported 3 ACCEPTED MANUSCRIPT 78 so far (von Reumont et al., 2014a). Remipedes have paired venom glands located in the first 79 segments of the cephalothorax and they use their paired fang-like maxillulae for venom delivery 80 (von Reumont et al., 2014a). 81 In contrast, venomous species in the other arthropod subphyla are common or in some lineages 82 even the most abundant representatives. Within the Myriapoda, the class Chilopoda contains 83 about 3500 species of venomous centipedes; these arthropods date back to at least 430 mya, 84 making their venom systems one of the oldest among terrestrial animals (Undheim et al., 2015). 85 For venom delivery, centipedes use their paired forcipules ("poison claws") containing the venom 86 glands, which evolved from the first pair of walking legs (Undheim et al., 2015). Within the 87 Chelicerata, venomous lineages have only developed in the class Arachnida, which comprises 88 four orders that have independently evolved venom systems: Acari (ticks), Araneae (true 89 spiders), Scorpiones (scorpions) and Pseudoscorpiones (pseudoscorpions). Within the Acari, ticks 90 have been recently considered as venomous ectoparasites due to the composition and function of 91 their saliva/venom (Cabezas-Cruz and Valdes, 2014), although this classification is not 92 unanimously accepted and might depend of the actual definition of the term “venom” that is used 93 (Pienaar et al., 2018). Tick saliva/venom is produced in the salivary glands and injected into the 94 host via a structure called the hypostome, which is used to penetrate the host’s epidermis and 95 helps in anchoring the tick while feeding (Pienaar et al., 2018). Pseudoscorpiones with their 96 venom glands being located in the fixed and/or the movable finger of their pedipalpal pincers 97 comprise about 3300 species worldwide (Murienne et al., 2008), but their small size has so far 98 limited research on their venoms. A little less diverse are the scorpions, with 2336 species known 99 to date (Rein, 2018) and all of them use venom. Their paired venom glands are located in the last 100 segment of the metasoma ("tail") and connected to a single stinger for venom injection (Yigit and 101 Benli, 2008). The most diverse of all arachnids are the spiders, which currently comprise over 102 47,000 species (World Spider Catalog, 2018). AllMANUSCRIPT spiders, with the exception of the family 103 Uloboridae (~ 0.6% of all spiders) are venomous, although in contrast to public opinion the vast 104 majority are not dangerous to humans (Hauke and Herzig, 2017). In mygalomorph spiders, the 105 paired venom glands are located in the basal part of the chelicerae, whereas in araneomorph 106 spiders they can extend into the prosoma (Foelix, 1992). Finally, the Hexapoda contain six 107 venomous orders of insects, including the hemimetabolous Hemiptera (bugs) and the 108 holometabolous Neuroptera (e.g. antlions), Hymenoptera (bees, wasps and ants), Diptera (flies), 109 Lepidoptera (butterflies and moths) and Coleoptera (beetles). Despite (or maybe because of) their 110 incredible diversity, insects are extremely under-represented in venom research. The best studied 111 order of venomous insects by far is Hymenoptera, although other hymenopteran venoms from 112 ants and wasps have also been studied (Moreau and Asgari, 2015; Touchard et al., 2016; Perez- 113 Riverol et al., 2017; Robinson et al., 2018). Dipterans are another insect order with several 114 different venomous lineages, but they have received far less attention compared to 115 hymenopterans. Venom in dipterans is used by adult members of the family Asilidae (robber 116 flies) and by larval Tabanidae (horse flies), Sciomyzidae (marsh flies), Cecidomyiidae (gall 117 midges) and Vermileonidae (von Reumont et al., 2014b). In coleopterans, a single cerambycid 118 species has been ACCEPTEDdescribed in which the adult beetle delivers (a possibly defensive) venom with 119 the tip of the antennae, which has been modified into a scorpion-like stinger (Berkov et al., 120 2008). In addition, some larval beetles also have venom glands that are used for prey capture (for 121 details see Walker et al., 2018c). 122 123 4 ACCEPTED MANUSCRIPT 124 125 126 2. Complexity of arthropod venom compositions 127 Venomous arthropods dwarf all other venomous organisms in both number and diversity, and 128 they also have some of the most complex venom compositions. Most arthropod venoms are 129 complex cocktails made up of water, salts, small bioactive molecules, peptides, enzymes and 130 larger proteins, with peptides or proteins usually comprising the majority of venom toxins. Some 131 spider venoms for example have been reported to contain > 1,000 peptide toxins (Escoubas et al., 132 2006). There are a number of reasons that might explain this incredible complexity of arthropod 133 venoms as summarized in Table 1.