Structure-function studies of the bacterial plasmid defence system Wadjet

Microbes are found in many environments, and in almost all cases are under constant attack from
bacteriophages and other selfish genetic elements. To avoid infection, bacteria have evolved a wide
range of defence mechanisms. These different systems are found clustered on the genome in what
are called "defence islands". The defence systems include the well-know restriction enzymes and
CRISPR-Cas9, which have been exploited for molecular biology and gene editing, respectively. Yet
there are many other uncharacterised systems within the defence islands that may provide yet more
tools for scientists to exploit. This project aims to use biophysical analysis and structural biology to
explore the mechanism of one such system, named after the Egyptian goddess Wadjet.
The Wadjet system prevents bacterial transformation by plasmids. It comprises four genes: jetA, jetB,
JetC and JetD. jetABC encode gene products that are related at a sequence level to bacterial
condensins. Condensins are widespread across all organisms, and are ATP-dependent molecular
machines that help to regulate the process of genome segregation during cell division. Their exact
mechanisms and roles are still debated. They form large protein complexes that use ATP hydrolysis to
drive large-scale changes in DNA conformation, including tethering DNA together, or actively
extruding DNA loops as molecular motors. In this collaborative project between the Szczelkun and
Berger-Schaffitzel labs, you will determine the overall structure of the Wadjet JetABCD complex, show
how it interacts with DNA, and determine the role for ATP hydrolysis. We propose that DNA capture
or loop extrusion blocks plasmid replication. These activities will be directly distinguished and
measured in real time using a single molecule magnetic tweezers assay.