Abstract
The plasmid partition protein KorB has a dual role: it is essential for the correct segregation of the low copy number broad host range RK2 plasmid while also being an important regulator of transcription. KorB belongs to the ParB family of proteins, and partitioning in RK2 has been studied as a simplified model of bacterial chromosome segregation. Structural information on full-length ParB proteins is limited, mainly due to the inability to grow crystals suitable for diffraction studies. We show, using CD and NMR, that KorB has regions of significant intrinsic disorder and hence it adopts a multiplicity of conformations in solution. The biophysical data are consistent with bioinformatic predictions based on the amino acid sequence that the N-terminal region and also the region between the central DNA-binding domain and the C-terminal dimerization domain are intrinsically disordered. We have used small angle x-ray scattering data to determine the ensemble of solution conformations for KorB and selected deletion mutants, based on models of the known domain structures. This conformational range of KorB is likely to be biologically required for DNA partitioning and for binding to a diverse set of partner proteins.
Highlights
The partitioning of DNA between daughter cells upon cell division is critical for the survival of all organisms
KorB has an additional N-terminal 20 amino acids compared with SpoOJ; it contains two additional predicted helices at the N terminus of the central domain, after the helix-turnhelix motif, which are not found in SpoOJ (Fig. 1B) [1]
As the first structural description of a full-length ParB protein, we have reconstructed KorB from the known crystal structures using small angle x-ray scattering (SAXS)5 and calculated an ensemble of conformations that the protein adopts in solution
Summary
Using a range of biophysical techniques we show the protein is modular in its domain organization and that the orientations of the domains of KorB within the protein are highly flexible due to zones of intrinsic disorder along the length of the protein. As the first structural description of a full-length ParB protein, we have reconstructed KorB from the known crystal structures using small angle x-ray scattering (SAXS) and calculated an ensemble of conformations that the protein adopts in solution. This flexibility will be important for the protein’s functional role in the cell enabling it to bind at different distances along DNA and to different binding partners [3,4,5,6, 9]
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