Lineage–specific amino acids define functional attributes of the protomer-protomer interfaces for the Rad51 and Dmc1 recombinases

Abstract

Most eukaryotes possess two Rad51/RecA family DNA recombinases that are thought to have arisen from an ancient gene duplication event: Rad51, which is expressed in both mitosis and meiosis; and Dmc1, which is only expressed in meiosis. To explore the evolutionary relationship between these recombinases, here, we present high-resolution CryoEM structures of S. cerevisiae Rad51 filaments and S. cerevisiae Dmc1 filaments bound to ssDNA, which reveal a pair of stacked interfacial aromatic amino acid residues that are nearly universally conserved in Rad51 but are absent from Dmc1. We use a combination of bioinformatics, genetic analysis of natural sequence variation, and deep mutational analysis to probe the functionally tolerated sequence space for these stacked aromatic residues. Our findings demonstrate that the functional landscape of the interfacial aromatic residues within the Rad51 filament is highly constrained. In contrast, the amino acids at the equivalent positions within the Dmc1 filament exhibit a broad functional landscape. This work helps highlight the distinct evolutionary trajectories of these two eukaryotic recombinases, which may have contributed to their functional and mechanistic divergence. AUTHOR SUMMARY: Most eukaryotic organisms have two closely related proteins, Rad51 and Dmc1, that are needed for different aspects of genetic recombination. These proteins may have evolved from a single gene that was duplicated during the early evolution of eukaryotes. Rad51 is active during both normal cell division (mitosis) and sexual reproduction (meiosis), while Dmc1 is only active during meiosis. To better understand how these proteins are related, we studied their three-dimensional structures using high resolution cryogenic electron microscopy. Our findings show that Rad51 has a specific set of conserved amino acids located at the protein interfaces, but this set of amino acids is different in Dmc1. We used a series of genetic approaches to analyze how these amino acids affect the proteins’ function. Our results show that Rad51 has a strict set of rules governing the identify of these amino acids, whereas Dmc1 does not. This research sheds light on how Rad51 and Dmc1 have evolved differently, leading to distinct functions in genetic recombination.