Ancient convergence with prokaryote defense and recent adaptations to lentiviruses in primates characterize the ancestral immune factors SAMD9s.

Human SAMD9 and SAMD9L are duplicated genes that encode innate immune proteins restricting poxviruses and lentiviruses, such as HIV, and implicated in life-threatening genetic diseases and cancer. Here, we combined structural similarity searches, phylogenetics and population genomics with experimental assays of SAMD9/9L functions to resolve the evolutionary and functional dynamics of these immune proteins, spanning from prokaryotes to primates. We discovered structural analogs of SAMD9/9L in the anti-bacteriophage defense system Avs, resulting from convergent evolution. Further, the predicted nuclease active site was conserved in bacterial analogs and was essential for cell death functions, suggesting a fundamental role in defense across different life kingdoms. Despite this ancestral immunity, we identified genomic signatures of evolutionary arms-races in mammals, with remarkable gene copy number variations targeted by natural selection. We further unveiled that the absence of SAMD9 in bonobos corresponds to a recent gene loss still segregating in the population. Finally, we found that chimp and bonobo SAMD9Ls have enhanced anti-HIV-1 functions, and that bonobo-specific SAMD9L polymorphisms confer increased anti-HIV-1 activity to human SAMD9L without compromising its effect on cell translation. These SAMD9/9L adaptations likely resulted from strong viral selective pressures, including by primate lentiviruses, and could contribute to lentiviral resistance in bonobos. Altogether, this study elucidates the interplay between ancient immune convergence across kingdoms and species-specific adaptations within the Avs9 and SAMD9/9L antiviral shared immunity.