Scientists ‘Couldn’t Believe’ First of Its Kind Evolutionary Accident

In a first, scientists have stumbled across a natural protein that follows a mathematical pattern of self-similarity called a fractal. The peculiar protein changes our understanding of self-assembly in nature and demonstrates the impressive potential of molecular evolution.

Fractals are a visual expression of a repeating pattern or formula that starts out simple and gets progressively more complex. These patterns can be found in nature, such as in the leaves of a fern or the spirals of a seashell. But fractals have never been seen at a molecular level. Until now.

“We stumbled on this structure completely by accident and almost couldn’t believe what we saw when we first took images of it using an electron microscope,” said the study’s first author, Franziska Sendker, in a statement.

“The protein makes these beautiful triangles and as the fractal grows, we see these larger and larger triangular voids in the middle of them, which is totally unlike any protein assembly we’ve ever seen before,” said Sendker, a postdoctoral researcher at Harvard Medical School and previously a researcher in evolutionary biochemistry at Germany’s Max Planck Institute.

The study’s results were published in the journal Nature on April 10.

The protein in question is a microbial enzyme, called citrate synthase, that is produced by a single-celled species of photosynthesizing bacteria. The enzyme itself is not rare—our bodies have their own version of citrate synthase that is involved in cellular energy production. However, this particular form of citrate synthase has a slightly different structure from our own, allowing it to spontaneously assemble into the unusual repeating pattern seen by the researchers.

Exactly why this protein evolved to produce this pattern is still unclear. In fact, the research team thinks that the infinitely intricate pattern may have formed by mistake.

To study whether this unusual shape might have some evolutionary purpose, the team genetically manipulated the bacteria to prevent their enzymes from forming this fractal shape. Surprisingly, these genetically modified bacteria grew just as well under a variety of different conditions.

“This prompted us to wonder whether this might just be a harmless accident of evolution,” evolutionary biologist and study co-author Georg Hochberg said in a statement. “Such accidents can happen when the structure in question isn’t too difficult to construct.”

He went on: “Although we can never be totally sure of the reasons why things happened in the past, this particular case does have all the trappings of a seemingly complex biological structure that just popped into existence for no good reason at all because it was simply very easy to evolve.”

The fact that something as complicated as a molecular fractal could emerge by accident through evolution suggests there may be more examples of these intricate patterns in molecular biology, hidden in plain sight.