Scientists reveal double life of sunflower enzyme

February 1, 2018, University of Western Australia
Scientists reveal double life of sunflower enzyme
Credit: University of Western Australia

Scientists have explained how a protein-cutting enzyme can join the ends of proteins together, creating protein circles; a finding with immediate applications in producing therapeutic drug treatments that is published in a study in the open access journal eLife.

The common enzyme at the centre of the study is from the common sunflower and leads a double life – able to cut proteins, but also join them together. Previously, the process from cutting to joining was not understood.

Researchers from The University of Western Australia and the University of Minnesota have at last provided a structural explanation of how sunflowers make super-stable rings and by inference, how the many other with circular proteins do it too.

The team and others around the world had previously shown the enzyme could cut proteins, and also that a few could join them together sometimes.

By making a protein crystal of the enzyme, the UWA-led team was able to look at the protein's shape in three dimensions and also saw a little bit of protein caught in the enzyme's 'jaws' – what's called a tetrahedral intermediate. This information, combined with experiments introducing mutations into the protein, explained how the enzyme takes a protein string and creates a protein ring with it.

The work is of interest to chemists and biotechnologists especially due to the current interest in the circularisation process for its use in generating a host of circular protein scaffolds that could be used as therapeutic drug treatments.

The study shows the crystal structure of an active form of the enzyme known as AEP (asparaginyl endo-peptidase) from sunflower seeds. The authors directly addressed the question of how AEPs actually produced circular proteins.

Lead author Dr. Joel Haywood, a research associate in UWA's School of Molecular Sciences said AEP enzymes were found in all plants and their best-known job was to defend plants from pathogens and to mature seed store proteins, but it was thought that some had specialised to produce circular proteins that were super-stable and rigid.

"Most scientists think these protein rings protect plants from pests," Dr. Haywood said.

"We were lucky to notice a tetrahedral intermediate in the structure. They're very rare, but extremely helpful as it's like catching the enzyme in the act of cutting and joining."

UWA lab head Dr. Joshua Mylne said what surprised the researchers was that seemingly any AEP could circularise proteins provided the enzyme was 'activated' properly and was given the right protein and conditions to circularise.

"We showed this using a couple AEPs from plants lacking circular proteins altogether," Dr. Mylne said.

"Now we've worked out how to crystallise these enzymes and how they work, we're looking how to use bacteria to cheaply create highly efficient enzymes."

Dr. Mylne led the team of Australian and US scientists that revealed the process through the Australian Research Council-supported study "Structural basis of ribosomal peptide macrocyclisation in plants."

Explore further: Sunflower protein 'scissors' provide sunny news for medicine

More information: Joel Haywood et al. Structural basis of ribosomal peptide macrocyclization in plants, eLife (2018). DOI: 10.7554/eLife.32955

Related Stories

Ancient buried treasure found in daisy seeds

March 31, 2014

( —By tracing the evolutionary origin of a drug-like protein ring found in sunflowers, Australian and US scientists have discovered a diverse, 18-million-year-old group of buried proteins in daisy seeds.

Cancer drug found hiding in sunflower seed protein

March 21, 2011

University of Queensland scientists have found sunflower proteins and their processing machinery are hijacked to make rogue protein rings in a discovery that could open the door to cheaper, plant-based drug manufacturing.

Proteins hiding in proteins take an evolutionary shortcut

March 27, 2017

How a drug-like protein ring evolved in sunflowers has been pieced together by Australian and US scientists in a study published in Molecular Biology and Evolution. Although the evolutionary process took some 45 million years, ...

Researchers report first 3-D structure of DHHC enzymes

January 11, 2018

The first three-dimensional structure of DHHC proteins—enzymes involved in many cellular processes, including cancer—explains how they function and may offer a blueprint for designing therapeutic drugs. Researchers have ...

New function in gene-regulatory protein discovered

October 20, 2017

Researchers at Umeå and Stockholm universities in Sweden and Johns Hopkins University School of Medicine in the U.S. have published a new study in the journal Molecular Cell. They show how the protein CBP affects the expression ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.