Chance and purpose in the evolution of protein complexes
Abstract: The role of chance has a rich and controversial history in evolutionary theory. On one side of the spectrum lies extreme adaptionism, which assigns purpose to all features of organisms, assuming that they are highly optimized by natural selection. Chance plays a minimal role in this view, because selection so powerful that it always finds globally optimal solutions. On the other side of the spectrum lies Stephen Jay Gould’s view that evolution is so dominated by random chance events, that if we were to ‘replay the tape of life’, evolution would take an almost unrecognizably different path from our own. We use the evolution of protein complexes as a model system to empirically study the role of chance and purpose in their evolution. Using ancestral sequence reconstruction and biochemical characterization of resurrected protein complexes I will show that a universal mutational ratchet entrenches and preserves protein complexes, even if they serve no functional purpose. Further, I will present a phylogenetic method to directly quantify the rate at which protein-protein interactions change due to chance alone and present data showing that this occurs at a remarkably uniform rate in a family of dimeric transcription factors. Taken together, these results imply that chance plays a surprising and important role in molecular evolution that makes evolution somewhat predictable on very long time-scales.
Host: Paul Rainey