Fast-paced evolution of proteins 

The de novo evolution of proteins is now considered a common route for biological innovation. It can involve the creation of a new protein via a new protein-coding gene that develops directly out of non-coding DNA, from frameshift mutations shifting the way a gene sequence is read, or from overprinting, which effectively involves two genes overlapping.

This collaborative research, involving scientists from the University of Western Australia, the University of Queensland, CSIRO, La Trobe University, the University of Tennessee and the University of Texas, documents how the PawS1 gene from the common sunflower (Helianthus annuus) actually evolved to encode for an additional peptide with novel biochemical functionality more than 18 million years ago.

To understand how this extra function was acquired, the researchers cloned PawS1 genes and identified the corresponding proteins in the seeds.

“This led to the discovery of a rapidly evolving family of tiny proteins that are super-stable and related to a protein discovered first in sunflowers and demonstrated subsequently to have potential as a drug for cancer,” said Professor Joshua Mylne from UWA who led the team of Australian and US scientists that revealed this new family of proteins.

The researchers showed that the PawS1 gene encodes for the precursor protein for albumin seed storage, preproalbumin, and a cyclic peptide, SFTI-1.

They went on to show that SFTI-1 arises from a sequence region usually discarded during albumin maturation, and has novel biochemical activity - it inhibits digestive enzymes. SFTI-1 also has a sequence motif homologous to unrelated inhibitors from legumes, cereals, and frogs.

“Although this work is of interest to researchers by providing an understanding of how new proteins can evolve from scratch, it also provides a ‘toolbox’ of peptides that drug designers can use to stabilise drugs.

Dr Alysha Elliott from UQ predicted the new family of seed proteins would be found in as many 4700 species of daisy.

“Conventional wisdom is that new proteins usually arise gradually,” Professor Mylne said. “Scientists are now beginning to realise that quite often, completely new proteins appear suddenly. Most of these studies are done with genes, but what we’ve done is work with the proteins the genes make too.

“What we’ve been able to do is propose the evolutionary steps that these rings had to undergo in order to be born.”

The study was recently published in Plant Cell