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Antimicrobial protein found in echidna milk

Lays the groundwork for antimicrobial resistance.

Alakananda Dasgupta

doi:10.1038/nindia.2019.80 Published online 24 June 2019

The echidna dubbed 'Big Mamma' who was part of the milking programme on Kangaroo Island in Australia.

© J. Sharp

A recent study1 has identified a novel antimicrobial protein (AMP) in the milk of echidna (Tachyglossus aculeatus), an oviparous or egg-laying mammal, found exclusively in Australia and New Guinea. The researchers says this naturally occurring protein could potentially be used for treatment of mastitis and other infections that affect humans and dairy animals.

Remarkably, despite being a mammal the echidna lays eggs, from which a very young echidna emerges, solely dependent on its mother’s milk for development.

The study is a collaborative effort between researchers at the Hyderabad-based Centre for Cellular and Molecular Biology and Deakin University, Australia. The lead author of the study, Satish Kumar, says they produced the protein Echidna AMP (EchAMP) in bulk using a bacteria-based protein expression system, and purified it. The purified recombinant EchAMP (rEchAMP) had significant antibacterial activity against a wide range of bacteria. 

This study was prompted by earlier work in which Julie Sharp and Kevin Nicholas of Deakin were looking for milk proteins in monotremes (mammals that lay eggs, but nurse their offspring with milk), which aid in development of the young.

The researchers obtained milked from an echidna dubbed ‘Big Mamma’ by injecting it with oxytocin, a hormone that triggers milk let down. However, the EchAMP used in the subsequent studies was generated using recombinant protein technology. Sharp says, “Among developmental proteins we also discovered the presence of AMPs.”

Earlier, Swathi Bisana, a graduate student of Kumar and Sharp, harvested milk cells from 'Big Mamma' to determine the nucleic acid sequence of their complementary DNA (cDNA). In genetics, cDNA is DNA synthesized from a single-stranded RNA in a reaction catalyzed by the enzyme reverse transcriptase. Bisana identified a novel gene specific to echidna, the EchAMP, and the corresponding peptide, EchAMP.

The current study confirms the antimicrobial properties of EchAMP suggested by Bisana. Also the recent paper explored a prokaryotic version of EchAMP (a simple unfolded version), which was purified, whereas Bisana had looked at the eukaryotic version of the protein. A prokaryote is a unicellular organism, such as a bacterium, that lacks a membrane- bound nucleus, mitochondria or any other membrane-bound organelle. Eukaryotes like plants, fungi, algae, animals and humans have these features.

The project is a pointer to how lactation functioned during the evolution of mammals. Bisana suggests that EchAMP may have an important role in protecting the vulnerable monotreme young in the pouch, and non-sterile burrow environments.

AMPs form part of the innate immune system — or the first line of defence against pathogens —and exhibit a very low predilection for resistance.

Bisana adds that as antibiotic resistance and superbugs are a looming crisis, EchAMP may offer solutions in combating some infections that affect humans and dairy animals. Sharp, however, says that AMPs are prone to degradation within the body, so this treatment may only have an application in topical treatments, such as creams. New methods need to be developed to protect AMPs if they are to be used in other applications.


References

1. Kumar, A. et al. Structural and mechanistic insights into EchAMP: A antimicrobial protein from the Echidna milk. Biochim Biophys Acta Biomembr. 1861, 1260–1274 (2019)