Term papers writing service


A review of the nature of the black widow spider

Received 2006 Sep 28; Accepted 2006 Nov 17. These toxins stimulate massive release of neurotransmitters from nerve terminals and act 1 by binding to specific receptors, some of which mediate an exocytotic signal, and 2 by inserting themselves into the membrane and forming ion-permeable pores.

Only tetramers have been observed to insert into membranes and form pores. Introduction Species of the genus Latrodectus Arthropoda: Indeed, its bites cause severe pain and other serious clinical symptoms in humans, making this spider medically important. Toxicity against vertebrates is likely to have evolved as a means to protect the species against predation and accidental crushing.

1. Introduction

The venom has also been shown, at least under laboratory conditions, to paralyse or kill crustaceans, some of which may actually be hunted by the spider. Latrodectus venom contains a rich cocktail of toxins latrotoxins and other biologically active substances, which affect the nervous system of victims. As such, the venom has served for decades as a source of important biological tools that have been used to dissect and study the molecular mechanisms of exocytosis in neurones and endocrine cells.

The insecticidal components of Latrodectus venom latroinsectotoxins, LITsin turn, have been looked at keenly by the chemical industry as potential pesticides, but remain relatively poorly understood, partly because they are more numerous, labile and difficult to purify than their vertebrate-specific counterpart. The complex venom Latrodectus venom is produced by glandular cells in the spider's chelicerae. In a process called holocrine secretion, these cells disintegrate and their content is released into the lumen of the gland Smith and Russell, 1966.

This yields a complex mixture of toxins, enzymes and other cellular constituents, and the purification of specific active components from this venom can be challenging. High and similar molecular masses of LTXs and their propensity to oligomerise and aggregate further exacerbate the difficulty. Therefore, it is advantageous to limit the starting material for purification and physiological studies to the soluble contents of the venom gland lumen see e.

  • It is believed that brown widows, which originated in Africa, may be competing with black widows, causing a decrease in the black widow population Vetter 2010;
  • The cleavage results in the removal of a 28- to 47-residue N-terminal leader sequence and of about 200 residues from the C-terminus.

However, most initial studies used crude buffer extracts from venom glands, and only relatively recently did venom suppliers start producing venom by milking spiders. For example, Fauna Laboratories Ltd. Another venom supplier, Alomone Labs Ltd. Venom application to various tissue preparations led to the general observation or implication of a strong increase in neurotransmitter secretion.

Bettini, 1971 ; Majori et al. Heating the venom resulted in loss of toxicity, indicating that its active components were proteins e. This was confirmed by pre-treatment of crude gland extracts with antiserum, which completely blocked the toxicity in cockroaches, ruling out a major role for small molecular weight substances, such as serotonin Majori et al. First attempts at purifying these proteins suggested the presence of several high molecular mass proteins, which seemed to act in a phylum-specific manner.

The first purification by column electrophoresis on cellulose powder Frontali and Grasso, 1964 gave three major fractions, of which two were toxic to house flies but had distinct effects, and one was active in guinea-pigs.

Insecticidal toxins from black widow spider venom

Later, a fourth fraction was found to be toxic to crustaceans Bettini, 1971. Further improvements in chromatographic matrices led to the purification by gel-filtration and subsequent ion-exchange chromatography Frontali et al. Interestingly, a set of 5-kDa proteins was also isolated by this method and shown to have a very rapid, but transient, paralytic activity in insects Ornberg et al.

  • In Florida, Latrodectus mactans Southern black widow , is found as well as Latrodectus geometricus brown widow , Latrodectus bishopi red widow , and Latrodectus variolus Northern black widow Edwards 2002;
  • Journal of Arachnology 13:

Subsequent systematic efforts of the Grishin group Krasnoperov et al. To date, black widow spider venom has been found to contain seven proteins with neurotoxic activity.

There are five insectotoxins: Four LTXs have been cloned: LMWPs are structurally related to crustacean hyperglycemic hormones and have molecular masses of 8 and 9. These peptides are non-toxic by themselves Gasparini et al. Purified LTXs have been consistently reported to act in a strictly phylum-specific manner e. Gundersen, personal communicationwhile retaining full toxicity for mammals.

It must also be stressed that venom preparations from different species, or sub-species, of Latrodectus often give very different chromatographic profiles cf. Frontali and Grasso, 1964 ; Frontali et al. There is also anecdotal evidence of local and even seasonal variations in venom contents Keegan et al. However, the principal components of different venoms seem to be very similar or indistinguishable by SDS-gel electrophoresis and immunological analysis.

For example, insectotoxins from even a distinct theridiid spider, Steatoda paykulliana, were shown to have the same immunological properties as the LITs from the L. Insectotoxins and their effects 3. Phenotypic manifestations Behavioural aspects of insect latrodectism are obviously scarcely monitored, let alone reported, but venom effects on cockroach behaviour have been investigated Franklin, 1988 and many symptoms were found to be similar to those described for humans.

For instance, limb hyperextension and jerking in cockroaches correspond to muscle rigidity, motor restlessness, cramps, and increase in tendon flexes in humans. Quivering in cockroaches resembles fibrillation of groups of muscle fibres near the site of a bite in humans, often followed by trembling and clonic contractions.

Cardiac block after a transient increase in the rate of heartbeat in Periplaneta americana is paralleled by tachycardia and hypertension in humans. Toxicity It is difficult to compare the published data on the toxicity of different LITs because preparations of variable purity have been tested on a diversity of insect species.

However, when five insectotoxins were later purified to homogeneity and tested on wax moth Galleria mellonella larvae Krasnoperov et al.

The other insectotoxins systematically studied in that work Krasnoperov et al. One explanation for these differences in toxicity could be the distinct target specificities of LITs.

On the other hand, the LITs may be differentially sensitive to specific procedures used for their isolation. Different neurotransmitter systems Physiological effects observed in insect tissue preparations on application of the whole venom or purified insecticidal fractions are consistent with a dramatic enhancement of transmitter secretion.

This vesicular release was dependent on the presence of intact SNARE proteins—synaptobrevin and syntaxin Broadie et al. Ultrastructural studies demonstrated loss of synaptic vesicles from some but not all synapses, as well as vesicle clumping Cull-Candy et al. In lobster NMJs Fritz et al. Latrodectus venom also affects the cholinergic sensory nervous system of insects. Venom application to the sixth abdominal ganglion from cockroach P.

Similar effects Neri et al. At least in the case of cockroach ganglion preparations, the venom can apparently access and stimulate the insect central nervous system Franklin, a review of the nature of the black widow spider. The sensitivity of insect central neurones to various fractions of black widow spider venom was further confirmed by monitoring release of acetylcholine from locust synaptosomes Knipper et al.

Therefore, in vertebrate neuromuscular preparations even whole black widow venom acts selectively on motor nerve terminals. In insect NMJs, in addition to the major presynaptic effect, the whole venom causes a clear, albeit minor, postsynaptic action Griffiths and Smyth, 1973.

In particular, the venom causes fluctuations of the muscle membrane potential almost immediately after its application, before there is any massive release of transmitter. These effects could be due to some venom components forming ion-permeable pores indiscriminately. Insectotoxins from the venom of a closely related spider S. However, all the effects can be blocked by specific antisera Majori et al.

This indicates that the toxins are not completely internalised and are still accessible from the extracellular space. A detailed structural analysis of LITs is required in order to interpret physiological effects and understand the molecular mechanisms of these toxins. Upon disintegration of secretory cells, the protoxins undergo proteolytic processing in the glandular lumen. The cleavage results in the removal of a 28- to 47-residue N-terminal leader sequence and of about 200 residues from the C-terminus.

As a result of this processing, LTXs become activated Kiyatkin et al.