PARMRC · Structural studies on the ParMRC plasmid DNA partitioning complex

The segregation of newly replicated DNA is an essential process in all prokaryotes and eukaryotes, ensuring the propagation of DNA to daughter cells. In bacteria, the plasmid partitioning system helps in the proper segregation of low copy number plasmids during cell division. The type II plasmid partitioning system (ParMRC) consists of three major elements – a parC DNA site, which acts as a centromeric region, and two proteins, one of which (ParR) binds to the centromeric region, and the filament-forming, actin-like protein ParM. The relative simplicity of the ParMRC plasmid partitioning system makes it an attractive model for studying DNA segregation. Although the ParMRC plasmid partitioning system has been characterized so as to provide an overview of the various complex structures formed, further structural studies using crystallography and cryo-electron microscopy can help in understanding the molecular mechanism of action. The activation of ParM and polymerization in the presence of ATP and the ParRC complex, de-polymerization in the presence of ADP and the dynamic instability of the filaments, and how these lead to the movement of the plasmids to the opposite ends of the cell are some of the mysteries that require investigation. The proposal tries to address the two key issues - i) conformational dynamics of ParM and mechanism of filament assembly, ii) interaction between ParRC complex and ParM. A few strategies that will be employed for tackling these problems through structural studies using a combination of crystallography and cryo electron microscopy are described. The proposed area of research will help the fellow to gain expertise in the field of cryo-electron microscopy, as well as contribute to the progress of the existing crystallographic work in the lab, following which independent work in the characterization of macromolecular complexes can be initiated in the home country.