Convergent evolution involving dimeric and trimeric dUTPases in pathogenicity island mobilization.

The dUTPase (Dut) enzymes, encoded by almost all free-living organisms and some viruses, prevent the misincorporation of uracil into DNA. We previously proposed that trimeric Duts are regulatory proteins involved in different cellular processes; including the phage-mediated transfer of the Staphylococcus aureus pathogenicity island SaPIbov1. Recently, it has been shown that the structurally unrelated dimeric Dut encoded by phage ϕNM1 is similarly able to mobilize SaPIbov1, suggesting dimeric Duts could also be regulatory proteins. How this is accomplished remains unsolved. Here, using in vivo, biochemical and structural approaches, we provide insights into the signaling mechanism used by the dimeric Duts to induce the SaPIbov1 cycle. As reported for the trimeric Duts, dimeric Duts contain an extremely variable region, here named domain VI, which is involved in the regulatory capacity of these enzymes. Remarkably, our results also show that the dimeric Dut signaling mechanism is modulated by dUTP, as with the trimeric Duts. Overall, our results demonstrate that although unrelated both in sequence and structure, dimeric and trimeric Duts control SaPI transfer by analogous mechanisms, representing a fascinating example of convergent evolution. This conserved mode of action highlights the biological significance of Duts as regulatory molecules.

Pirating conserved phage mechanisms promotes promiscuous staphylococcal pathogenicity island transfer.

Targeting conserved and essential processes is a successful strategy to combat enemies. Remarkably, the clinically important Staphylococcus aureus pathogenicity islands (SaPIs) use this tactic to spread in nature. SaPIs reside passively in the host chromosome, under the control of the SaPI-encoded master repressor, Stl. It has been assumed that SaPI de-repression is effected by specific phage proteins that bind to Stl, initiating the SaPI cycle. Different SaPIs encode different Stl repressors, so each targets a specific phage protein for its de-repression. Broadening this narrow vision, we report here that SaPIs ensure their promiscuous transfer by targeting conserved phage mechanisms. This is accomplished because the SaPI Stl repressors have acquired different domains to interact with unrelated proteins, encoded by different phages, but in all cases performing the same conserved function. This elegant strategy allows intra- and inter-generic SaPI transfer, highlighting these elements as one of nature's most fascinating subcellular parasites.

Another look at the mechanism involving trimeric dUTPases in Staphylococcus aureus pathogenicity island induction involves novel players in the party.

We have recently proposed that the trimeric staphylococcal phage encoded dUTPases (Duts) are signaling molecules that act analogously to eukaryotic G-proteins, using dUTP as a second messenger. To perform this regulatory role, the Duts require their characteristic extra motif VI, present in all the staphylococcal phage coded trimeric Duts, as well as the strongly conserved Dut motif V. Recently, however, an alternative model involving Duts in the transfer of the staphylococcal islands (SaPIs) has been suggested, questioning the implication of motifs V and VI. Here, using state-of the-art techniques, we have revisited the proposed models. Our results confirm that the mechanism by which the Duts derepress the SaPI cycle depends on dUTP and involves both motifs V and VI, as we have previously proposed. Surprisingly, the conserved Dut motif IV is also implicated in SaPI derepression. However, and in agreement with the proposed alternative model, the dUTP inhibits rather than inducing the process, as we had initially proposed. In summary, our results clarify, validate and establish the mechanism by which the Duts perform regulatory functions.

Virus Satellites Drive Viral Evolution and Ecology.

Virus satellites are widespread subcellular entities, present both in eukaryotic and in prokaryotic cells. Their modus vivendi involves parasitism of the life cycle of their inducing helper viruses, which assures their transmission to a new host. However, the evolutionary and ecological implications of satellites on helper viruses remain unclear. Here, using staphylococcal pathogenicity islands (SaPIs) as a model of virus satellites, we experimentally show that helper viruses rapidly evolve resistance to their virus satellites, preventing SaPI proliferation, and SaPIs in turn can readily evolve to overcome phage resistance. Genomic analyses of both these experimentally evolved strains as well as naturally occurring bacteriophages suggest that the SaPIs drive the coexistence of multiple alleles of the phage-coded SaPI inducing genes, as well as sometimes selecting for the absence of the SaPI depressing genes. We report similar (accidental) evolution of resistance to SaPIs in laboratory phages used for Staphylococcus aureus typing and also obtain the same qualitative results in both experimental evolution and phylogenetic studies of Enterococcus faecalis phages and their satellites viruses. In summary, our results suggest that helper and satellite viruses undergo rapid coevolution, which is likely to play a key role in the evolution and ecology of the viruses as well as their prokaryotic hosts.

dUTPases, the unexplored family of signalling molecules.

Deciphering the molecular mechanisms that control relevant cellular processes is of utmost importance to understand how viruses, prokaryotic and eukaryotic cells work. The diversity of living organisms suggests that there are novel regulators still to be discovered, which may uncover new regulatory paradigms. dUTPases (Duts) are assumed to be ubiquitous enzymes regulating cellular dUTP levels to prevent misincorporation of uracil into DNA. Recently however, Duts have been involved in the control of several relevant cellular processes, including transfer of mobile genetic elements, regulation of the immune system, autoimmunity or apoptosis, suggesting that they perform regulatory functions. This review aims at investigating the unexplored impact of Duts as novel signalling molecules.

Phage dUTPases control transfer of virulence genes by a proto-oncogenic G protein-like mechanism.

dUTPases (Duts) have emerged as promising regulatory molecules controlling relevant cellular processes. However, the mechanism underlying this regulatory function remains enigmatic. Using staphylococcal pathogenicity island (SaPI) repression as a model, we report here that phage Duts induce the transfer of SaPI-encoded virulence factors by switching between active (dUTP-bound) and inactive (apo state) conformations, a conversion catalyzed by their intrinsic dUTPase activity. Crystallographic and mutagenic analyses demonstrate that binding to dUTP reorders the C-terminal motif V of the phage-encoded Duts, rendering these proteins into the active conformation required for SaPI derepression. By contrast, the conversion to the apo state conformation by hydrolysis of the bound dUTP generates a protein that is unable to induce the SaPI cycle. Because none of the requirements involving Duts in SaPI transfer are exclusive to the phage-encoded proteins, we propose that Duts are widespread cellular regulators acting in a manner analogous to the eukaryotic G proteins.