Cell Calcium 52 (2012) 234–240 Contents lists available at SciVerse ScienceDirect Cell Calcium jo u rn al hom epa ge: www.elsevier.com/locate/ceca Presynaptic neurotoxins: An expanding array of natural and modified molecules Bazbek Davletov a,* , Enrico Ferrari a , Yuri Ushkaryov b a Medical Research Council Laboratory of Molecular Biology, Cambridge, UK b Medway School of Pharmacy, University of Kent, Chatham Maritime, UK a r t i c l e i n f o Article history: Received 15 February 2012 Received in revised form 4 May 2012 Accepted 13 May 2012 Available online 1 June 2012 Keywords: Botulinum Clostridial Neurotoxin Latrotoxin Chimera SNARE proteins Black widow spider Exocytosis Neurotransmitter release Presynaptic Calcium a b s t r a c t The process of neurotransmitter release from nerve terminals is a target for a wide array of presy- naptic toxins produced by various species, from humble bacteria to arthropods to vertebrate animals. Unlike other toxins, most presynaptic neurotoxins do not kill cells but simply inhibit or activate synap- tic transmission. In this review, we describe two types of presynaptic neurotoxins: clostridial toxins and latrotoxins, which are, respectively, the most potent blockers and stimulators of neurotransmitter release. These toxins have been instrumental in defining presynaptic functions and are now widely used in research and medicine. Here, we would like to analyse the diversity of these toxins and demonstrate how the knowledge of their structures and mechanisms of action can help us to design better tools for research and medical applications. We will look at natural and synthetic variations of these exquisite molecular machines, highlighting recent advances in our understanding of presynaptic toxins and ques- tions that remain to be answered. If we can decipher how a given biomolecule is modified by nature to target different species, we will be able to design new variants that carry only desired characteris- tics to achieve specific therapeutic, agricultural or research goals. Indeed, a number of research groups have already initiated a quest to harness the power of natural toxins with the aim of making them more specifically targeted and safer for future research and medical applications. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction As their name suggests, presynaptic neurotoxins target presy- naptic terminals where they affect the release of neurotransmitters. First, we would like to describe the presynaptic release mecha- nisms which were deciphered with the help of these presynaptic toxins. Neurotransmitters are stored in synaptic vesicles within the presynaptic terminal, and their release involves calcium-triggered fusion of the vesicular and presynaptic membranes (Fig. 1). Since both membranes are negatively charged, their repulsion can only be overcome by protein-mediated mechanisms. Presynaptic pro- teins which facilitate priming and fusion are known as SNARE proteins, an acronym for Soluble NSF Attachment protein Recep- tors, where NSF is an intracellular enzyme called N-ethylmaleimide Sensitive Factor [1]. Initially, one SNARE protein is found on the vesicular membrane (synaptobrevin also known as VAMP, for vesicle-associated membrane protein), whereas two other SNARE proteins – syntaxin and SNAP-25 – reside in the presynaptic mem- brane [2]. The three SNARE proteins undergo a series of priming events, which allow them to come into close contact between the membranes [3]. In response to Ca 2+ entry into the presynaptic * Corresponding author. Tel.: +44 1223 402009. E-mail address: bazbek@mrc-lmb.cam.ac.uk (B. Davletov). terminal, SNARE proteins undergo a coiling reaction facilitating membrane interaction and fusion [2] leading to the release of intravesicular neurotransmitter into the extracellular space. After the release event completed, the SNARE proteins are uncoiled by the NSF enzyme [1] and the vesicle is retrieved – endocytosed – for refilling with a new load of neurotransmitter. As these fine molecular mechanisms, constituting the basis of neuronal communication, were developing in evolution, they also became a target for toxins produced by organisms from all taxa: bacteria, plants, molluscs, spiders, insects and vertebrates. Aimed at disabling the animal nervous system, neurotoxins have co-evolved with it to become sophisticated and powerful ‘magic bullets’, exquisitely targeting individual molecular components in presy- naptic nerve terminals. Their precise targeting of the presynaptic machinery has made neurotoxins the tools of choice for researchers trying to understand neurotransmitter release mechanisms [4]. Depending on their principal activity, presynaptic neurotoxins can be divided into two groups: inhibitory and excitatory, with the majority of neurotoxins falling into the first group. In addition, toxins can be classified by their main functional target: some neu- rotoxins perturb the mechanisms of vesicle fusion; the others affect cytosolic Ca 2+ – the trigger for neurotransmitter release. In this review, we will look at the most polar representatives of the different groups of presynaptic neurotoxins: the strongest inhibitors of vesicle fusion and the most potent activators of 0143-4160/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ceca.2012.05.006