Scientists find a naturally occurring molecule that forms a fractal

Fractals are everywhere in nature, from river deltas to tree branches. These structures look similar from afar as when you zoom in close. Certain fractals, called regular fractals, are identical on different scales and include whirls of Romanesco cauliflower (SN: 7/8/21). But regular fractals hadn’t been spotted in nature on the molecular level — until now.

A protein found in the bacterium Synechococcus elongatus assembles itself into a fractal called a Sierpiński triangle, evolutionary biochemist Georg Hochberg and colleagues report April 10 in Nature. When placed in water, the proteins linked up into triangles made up of smaller triangles, consisting of as many as 54 individual proteins, and potentially even more.

Researchers have previously designed synthetic molecules that can form regular fractals. But the bacterial protein, called citrate synthase, is the first with such fractal flair to be discovered in nature.

The scientists couldn’t identify any practical purpose for the pattern and concluded that it’s an evolutionary accident. Accidents occur in other assemblies of proteins, too. “Different kinds of complex-looking structures come and go on evolutionary timescales, sometimes with a use, sometimes without one,” says Hochberg, of the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany. “Their symmetry can be beguiling to us, and that’s why we think they have meaning.”