Ant venom: Protein and peptide profiles
- Published: Mar 16, 2017
- Author: Steve Down
- Channels: Proteomics & Genomics / Proteomics
Image: Hans Hillewaert.
In the ongoing quest for natural compounds that can be utilised as pharmaceuticals, antimicrobial compounds, pesticides and insect repellents, many research groups around the world are targeting plants because of their exploitation as traditional medicines. However, various groups of animals are also potential sources of active compounds, especially those which deploy venom like snakes, frogs, spiders, bees and cone snails.
Another creature which has been explored is the ant. There are estimated to be more than 16,000 species of ant around the world but the ones generating interest are those that can sting, whether in defence or when attacking prey. There are hundreds of peptides and proteins in ant venom but very little research has been carried out to determine which ones are the active species. Peptides with antimicrobial and pesticidal properties have been discovered in the venom of Neoponera goeldii, a South American ant, but a different ant from the same continent has been attracting the attention of an international team of researchers.
Graham Nicholson from the University of Technology Sydney, with coresearchers from the University of Antilles in French Guiana, the University of Toulouse, and VenomeTech, Valbonne, France, wanted to study the venom of Paraponera clavata, known as the bullet ant or the giant tropical ant, which is about one inch long. It is feared for its vicious sting, reckoned to be the worst of any Hymenoptera, a family which includes ants, bees, wasps and sawflies.
The powerful venom is toxic to both vertebrates and invertebrates but only one toxic neuropeptide, poneratoxin, has been studied to date. The research team decided to take a wide-ranging look at the peptides and proteins in the venom to see if the ant world could help mankind by presenting new bioactive compounds.
Electrical stimulation vs. dissection
As you might imagine, collecting sufficient venom from ants for a proteomics study can be challenging and two principal procedures have been used conventionally in the past. Nicholson decided to compare them with each other to see if the they influenced the peptide/protein profiles.
Ants found in one colony were separated into two random groups and venom was extracted by both methods. In the first, the venom glands were dissected, pooled and centrifuged in aqueous acetonitrile. In the second, individual ants were placed in a glass insert and electrically stimulated with a pair of tweezers attached to the abdomen. Ants were also collected from a second colony nearby and processed by venom gland dissection.
All three extracts were separated into different fractions by HPLC to reduce their complexity before further analysis. The chromatograms for the electrically stimulated and dissected samples from the same colony were very similar, with 39 fractions each, but that from the second colony had a very different profile with only 29 peaks.
The peptides were identified by matrix-assisted laser desorption/ionisation mass spectrometry while the proteins were first fractionated by 2D gel electrophoresis before digestion with the enzyme trypsin and analysis by liquid chromatography/mass spectrometry.
Complex peptide and protein profiles
The peptide profiles of the venoms were similar for the two collection modes, a large number being found with molecular masses up to 4000 Da. However, more peptides were detected following dissection, probably because parts of the gland were also removed.
Despite the similar profiles and mass distributions, in practice there was limited overlap between the individual peptides from dissection and electrical stimulation. A total of 309 peptides were detected but only 22 were common to the two extraction procedures.
When the proteins were examined, there was far more similarity between the collection methods with a commonality of 73%: out of 73 and 75 proteins identified in venom from electrical stimulation and dissection, 54 were found in both sets. The most abundant proteins were homologues of phospholipase A2, which is a common toxin in venoms of wasps, ants, bees and snakes and a major allergen in Hymenoptera. Apart from toxins, structural proteins and others related to cell regulation, transport and metabolism were identified.
The peptide and protein profiles of the ants in the second colony were not the same as those in the first, increasing the venom complexity and showing that even small geographical variations can have a marked effect on the venom composition.
The results illustrate the variability and rich composition of the venom from P. clavata but also show that the venom collection method changes the peptide/protein profile. The researchers preferred electrical stimulation to dissection as it delivers the major proteins without killing the ants. Since individual milking is inefficient for broad studies, they recommended a mass milking technique.
However, in order to have the best chance of finding active compounds as candidates for drugs, antimicrobial compounds and pesticides, both venom extraction protocols should be followed, due to the varying peptide profiles that they deliver.
Journal of Proteome Research 2017, 16, 1339-1351: "Combined peptidomic and proteomic analysis of electrically stimulated and manually sissected venom from the South American bullet ant Paraponera clavata"
Article by Steve Down
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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