The C-terminal domain of HpDprA is a DNA-binding winged helix domain that does not bind double-stranded DNA

DprA recruits ComM to facilitate recombination during natural transformation in Gram-negative bacteria

Natural transformation (NT) represents one of the major modes of horizontal gene transfer in bacterial species. During NT, cells can take up free DNA from the environment and integrate it into their genome by homologous recombination. While NT has been studied for >90 years, the molecular details underlying this recombination remain poorly understood. Recent work has demonstrated that ComM is an NT-specific hexameric helicase that promotes recombinational branch migration in Gram-negative bacteria. How ComM is loaded onto the post-synaptic recombination intermediate during NT, however, remains unclear. Another NT-specific recombination mediator protein that is ubiquitously conserved in both Gram-positive and Gram-negative bacteria is DprA. Here, we uncover that DprA homologs in Gram-negative species contain a C-terminal winged helix domain that is predicted to interact with ComM by AlphaFold. Using Helicobacter pylori and Vibrio cholerae as model systems, we demonstrate that ComM directly interacts with the DprA winged-helix domain, and that this interaction is critical for DprA to recruit ComM to the recombination site to promote branch migration during NT. These results advance our molecular understanding of recombination during this conserved mode of horizontal gene transfer. Furthermore, they demonstrate how structural modeling can help uncover unexpected interactions between well-studied proteins to provide deep mechanistic insight into the molecular coordination required for their activity.

SIGNIFICANCE STATEMENT

Bacteria can acquire novel traits like antibiotic resistance and virulence through horizontal gene transfer by natural transformation. During this process, cells take up free DNA from the environment and integrate it into their genome by homologous recombination. Many of the molecular details underlying this process, however, remain incompletely understood. In this study, we identify a new protein-protein interaction between ComM and DprA, two factors that promote homologous recombination during natural transformation in Gram-negative species. Through a combination of bioinformatics, structural modeling, cell biological assays, and complementary genetic approaches, we demonstrate that this interaction is required for DprA to recruit ComM to the site of homologous recombination.

Natural Transformation in Deinococcus radiodurans: A Genetic Analysis Reveals the Major Roles of DprA, DdrB, RecA, RecF, and RecO Proteins

Horizontal gene transfer is a major driver of bacterial evolution and adaptation to environmental stresses, occurring notably via transformation of naturally competent organisms. The Deinococcus radiodurans bacterium, characterized by its extreme radioresistance, is also naturally competent. Here, we investigated the role of D. radiodurans players involved in different steps of natural transformation. First, we identified the factors (PilQ, PilD, type IV pilins, PilB, PilT, ComEC-ComEA, and ComF) involved in DNA uptake and DNA translocation across the external and cytoplasmic membranes and showed that the DNA-uptake machinery is similar to that described in the Gram negative bacterium Vibrio cholerae. Then, we studied the involvement of recombination and DNA repair proteins, RecA, RecF, RecO, DprA, and DdrB into the DNA processing steps of D. radiodurans transformation by plasmid and genomic DNA. The transformation frequency of the cells devoid of DprA, a highly conserved protein among competent species, strongly decreased but was not completely abolished whereas it was completely abolished in ΔdprA ΔrecF, ΔdprA ΔrecO, and ΔdprA ΔddrB double mutants. We propose that RecF and RecO, belonging to the recombination mediator complex, and DdrB, a specific deinococcal DNA binding protein, can replace a function played by DprA, or alternatively, act at a different step of recombination with DprA. We also demonstrated that a ΔdprA mutant is as resistant as wild type to various doses of γ-irradiation, suggesting that DprA, and potentially transformation, do not play a major role in D. radiodurans radioresistance.