Abstract

Since the advent of DNA sequencing, the main tool for understanding evolution has been the analysis of DNA and the proteins encoded by the DNA . With the revolution in resolution that occurred in cryo-EM ~ 10 years ago, cryo-EM has now emerged as the main technique for determining the atomic structure of proteins, nucleoprotein complexes, and macromolecular assemblies. We have known for some time that sequences diverge more rapidly than structures, and thus examining structures can give insights into evolutionary relations that cannot yet be deduced at the level of sequences. I will show, using examples of bacterial and archaeal flagella, bacterial and archaeal pili, and archaeal viruses how very deep evolutionary relations may be deduced at the level of structures. Further, I will show how ubiquitous prokaryotic surface filaments, pili and flagella, have undergone a surprising divergence due to adaptations to very different environments. It has been the ability of these structures to adapt that accounts for their ubiquity.