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Frog skin protein may help fight superbugs
Proteins secreted by frog skin could one day help in the design of new antibiotics to fight superbugs, say researchers.

Biophysicist Dr Anton Le Brun, of the Australian Nuclear Science and Technology Organisation, and colleagues, report some of their work online in the European Biophysical Journal.

A few species of frogs are known to secrete peptides that protect against a broad range of unwanted bacteria.

The proteins are maculatin, from the green-eyed tree frog, and aurein, from the growling grass frog and the green and golden bellfrog.

Each protein has a unique way of killing bacteria by breaking their membranes, says Le Brun.

In research led by Professor Frances Separovic of the University of Melbourne, he and other colleagues used a device at the OPAL research reactor in Sydney to take a close-up look at the way in which maculatin and aurein do this.

They point out that no frogs were harmed in the research.

Instead, the research team used synthetic membranes and synthetic versions of the frog skin peptides. They used one membrane that mimicked a bacterial membrane, and another that mimicked a red blood cell membrane.

They wanted to look at the impact of the peptides on red cell membranes to ensure that they only damage bacterial cells and leave the animal cells untouched.

Using a device called a neutrons reflectometer the researchers studied exactly how and where the peptides bind to membranes.

"If you use microscopy you can see the surface of the membrane, but reflectivity allows us to probe underneath that surface - a membrane is 5 to 6 nanometres thick," says Le Brun.

The researchers found that maculatin, the longer peptide, spans the bacterial membrane, punches a hole in it, and changes its structure.

On the other hand, the shorter peptide, aurein, inserts itself into just part of the bacterial membrane.

Bacterial membranes have a negative charge on them which interact with the positively charged proteins, whereas animal cell membranes don't, says Le Brun.

He says neither protein significantly affected the synthetic animal cell membrane.

The next step is to use this knowledge to design new antibiotics, says Le Brun.

He says unlike current antibiotics, which tend to attack specific functions of the bacterial cell, peptides attack the bacterial membrane.

"That makes it more difficult for the bacterial to develop resistance to them," says Le Brun.

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