Shirley Temple, rattlesnakes and platypuses feature in antibiotic research
Two teams find promising proteins from unlikely sources. Andrew Masterson reports.
Rattlesnake venom and platypus milk are providing researchers with new germ-fighting molecules that open the door to the development of much-needed treatments to combat antibiotic resistant bacteria.
The fragment, named Ctn[15–34], is derived from a protein called crotalicidin (Ctn), which had earlier been identified as being effective against microbes, tumour cells and fungi. Unfortunately, being derived from the snake’s famously effective venom, it also inflicts a lot of damage to healthy cells.
Research published in 2016 established that Ctn[15–34] retained antimicrobial and anti-tumour properties, but did less damage to healthy tissue and also stayed stable in a serum.
In the latest paper, a team led by David Andreu of Pompeu Fabra University in Barcelona, Spain, reports on the precise mechanism by which crotalicidin and its derived fragment attack bacteria.
Andreu and his colleagues tested the molecules on common human pathogens Escherichia coli and Pseudomonas aeruginosa. They found that both proteins killed 90% of the bacteria – within two hours in the case of E.coli, and in half an hour for P. aeruginosa.
Both proteins worked by accumulating on the surface of the microbes, rendering them permeable. Crotalicidin worked more slowly, and in more complex ways, while Ctn[15–34] mounted a more direct attack and showed a preference for attaching to structures that resembled bacteria or tumour cells.
“The peptide is positive while the bacteria is negative, allowing it to kill the bacteria by inserting and disrupting the membrane,” says co-author Sonia Troeira Henriques from the University of Queensland in Australia.
“Because the cells in the body hosting the infection are neutral, they are not disrupted.”
The researchers conclude that Ctn[15–34], in particular, represents a promising target for drug development.
Equally promising, in its own way, is a novel protein discovered in the milk of Australia’s iconic egg-laying mammal, the platypus (Ornithorhynchus anatinus).
A team derived from research organisation CSIRO and Deakin University in Melbourne has used a high-tech synchrotron and crystallography to reproduce monotreme lactation protein (MLP), a molecule found only in platypus milk.
As early as 2010, researchers realised that the milk had powerful antibacterial properties, but now the CSIRO’s Janet Newman and her colleagues have found out why.
By analysing the milk, they discovered MLP, and were then able to build it step by step in the laboratory. Having done so, they set about deconstructing it, hunting for its secret.
What they found was a 3D structure never seen before – a protein shaped like a ringlet, which Newman’s team decided to name Shirley Temple, after the 1950s child movie star.
The scientists suggest that the development of the potent antimicrobial is a consequence of the platypus’s unique mothering style.
The species, like all mammals, produces milk, but unlike most it does not have teats. Instead, milk is secreted through skin pores, rather like sweat, and the hatched young consume it by licking. This means that the milk is exposed to a microbially diverse and possibly dangerous environment before it is swallowed – making a strong defence against bugs a very good idea.
Like the rattlesnake protein, MLP will very likely provide impetus for the refinement of new antibiotics and other medications.