Biochemical basis of Exo70 specialization

Molecular machines comprised by multiple subunits govern essential processes in the cell. Understanding how these complexes evolve is crucial to comprehend the evolution of cellular complexity. However, our understanding on the molecular mechanisms that allow multimeric complexes to change and acquire new functions is still limited. Here we used the plant exocyst complex as a model to study the evolution and mechanistic basis of neo-functionalization in multimeric protein complexes. By leveraging a combination of cell biology, proteomics, biochemistry, and phylogenetic analysis, we show the N-terminal domain of a single exocyst subunit, Exo70, have reverted its electrostatic charge over the course of evolution. This rendered a loose interaction with the rest of the complex and allowed Exo70 to rapidly diversify and acquire novel functions in plants. Our finding shows a novel model in which a single subunit scape from the evolutionary constrains of being in a complex, resulting in high diversification rates and neo-functionalization.