Molecular insights on SaPI inducing mechanism

Abstract del póster presentado al 8th Congress of European Microbiologist. FEMS 2019. Glasgow, Scotland. 7-11 July 2019(Póster. PM296) Background: S. aureus pathogenicity islands (SaPIs) are parasitic mobile genetic elements that exploit phages for induction and transfer. SaPIs integrate to the host chromosome and are repressed by Stl, the SaPI master regulator. SaPI induction is occurred when the SaPI Stl/DNA complex is disrupted via a specific protein encoded by helper phage. The inducer for SaPI1 is a phage protein called Sri. Interestingly, and in addition to SaPI1 de-repression, Sri blocks bacterial DNA replication by binding to the helicase loader protein (DnaI). Objectives: The fact that a small protein like Sri (52aa) interacts with two unrelated proteins raises several interesting questions; are DnaI and Stl sharing similar structural conformations being recognized by the same interacting residues on Sri, or by contrast, Sri has two interacting faces, one to interact with DnaI and the other to interact with Stl? Unraveling those questions would define SaPIs nature. If the DnaI and Stl share a conserved domain or similar fold, SaPIs would be then considered as phage parasites. By contrast, if Sri has two different interacting regions, this would imply in somehow that SaPIs can provide unrecognized advantages for the phage. Methods: To solve the above questions, in vivo and in vitro methods have been used including molecular, biochemical and protein crystallography techniques. Results: Our results provide insights on the mechanism that is used by SaPI1 to interact with Sri protein, highlighting these elements as one of the most fascinating mobiles genetic elements i