Edward H. Egelman, PhD, of the University of Virginia School of Medicine, and his collaborators have used cryo-electron microscopy to reveal how bacteria can move -- ending a mystery of more than 50 years. Egelman's prior imaging work saw him inducted into the prestigious National Academy of Sciences, one of the highest honors a scientist can receive. Credit: Dan Addison, University of Virginia Communications
Bacteria, such as E. coli, move around by using corkscrew-like flagella to propel themselves forward. Exactly how the thousands of identical protein subunits that form flagella come together to form this coiled structure has long been a mystery, although models for how these shapes might form have existed for decades. Now, an international team led by University of Virginia Health System researchers has unveiled how bacterial flagella achieve their “supercoiled” shape, using cryo-electron microscopy (cryo-EM) to resolve the details of flagellar filaments at the atomic level.
Cryo-EM examination of the atomic structure of the filaments that make up bacterial flagella revealed that the protein that forms them can exist in 11 different states. The corkscrew structure of the supercoiled flagellum results from a precise mixture of these different states. The team further examined the flagellar filaments of archaea using cryo-EM, and discovered that this separate domain of organisms achieves a similar supercoiled geometry with 10 different protein states. The results suggest that convergent evolution may be responsible for the similarities in form and function of bacterial and archaeal flagella. This research was published in the journal Cell.
“While models have existed for 50 years for how these filaments might form such regular coiled shapes, we have now determined the structure of these filaments in atomic detail,” said Edward H. Egelman, who led the study. “We can show that these models were wrong, and our new understanding will help pave the way for technologies that could be based upon such miniature propellers.”
Data from the microscopy experiments allowed the researchers to construct new detailed atomic models and visualizations of bacterial and archaeal flagellar filaments. The atomic structures revealed by the advanced cryo-EM technique both further understanding of the locomotion of many microorganisms and serve as a potential blueprint for future bio-inspired supercoil structures.