An international team of researchers, led by groups from the Max Planck Institute in Marburg and the Philipps University in Marburg, has made a remarkable discovery in molecular biology. They have identified the first regular molecular fractal in nature, found within a microbial enzyme called citrate synthase from a cyanobacterium. This enzyme spontaneously assembles into a pattern known as the Sierpinski triangle, a fractal structure that repeats itself across multiple scales. The study, published in Nature, sheds light on the rare occurrence of regular fractals in nature and the unique characteristics of this molecular assembly.

Fractals are patterns that exhibit self-similarity across various length scales. While they are common in macroscopic structures such as snowflakes and fern leaves, regular fractals that precisely match across scales are exceptionally rare. The discovery of a regular molecular fractal challenges the conventional understanding of molecular structures and their self-assembly processes.

The team’s findings reveal that the citrate synthase enzyme from the cyanobacterium Synechococcus elongatus forms the Sierpinski triangle, a pattern consisting of infinitely repeating triangles made up of smaller triangles. This unexpected discovery was made possible through electron microscopy and evolutionary biochemistry studies, which provided insights into the unique characteristics of this molecular assembly.

The researchers also delved into the evolutionary origins of this molecular fractal, uncovering that the assembly emerged through a violation of the rule of symmetry in protein self-assembly. Unlike typical symmetrical interactions that lead to smooth patterns on large scales, the citrate synthase enzyme’s assembly exhibited asymmetry, forming the Sierpinski triangle with its distinctive internal voids.

Furthermore, the team explored the physiological significance of this fractal assembly and found that while it can regulate the enzymatic activity of citrate synthase in vitro, it may not serve a specific physiological function in vivo. This led the researchers to consider that the fractal assembly could have emerged as a harmless evolutionary accident, as indicated by their ancestral sequence reconstruction experiments.

References

• Max Planck Society. (2024, April 11). Discovery of the first fractal molecule in nature. Phys.org. https://phys.org/news/2024-04-discovery-fractal-molecule-nature.html
• Sendker, F. L., Lo, Y. K., Heimerl, T., Bohn, S., Persson, L. J., Mais, C.-N., Sadowska, W., Paczia, N., Nußbaum, E., del Carmen Sánchez Olmos, M., Forchhammer, K., Schindler, D., Erb, T. J., Benesch, J. L. P., Marklund, E. G., Bange, G., Schuller, J. M., & Hochberg, G. K. A. (2024). Emergence of fractal geometries in the evolution of a metabolic enzyme. Nature, 1–7. https://doi.org/10.1038/s41586-024-07287-2