Abstract
Spo0J (stage 0 sporulation protein J, a member of the ParB superfamily) is an essential component of the ParABS (partition system of ParA, ParB and parS DNA) related bacterial chromosome segregation system. ParB (partition protein B) and its regulatory protein, ParA (partition protein A), act cooperatively through parS (partition S) DNA to facilitate chromosome segregation. ParB binds to chromosomal DNA at specific parS sites as well as the neighboring non-specific DNA sites. Various ParB molecules can associate together and spread along the chromosomal DNA. ParB oligomer and parS DNA interact together to form a high order nucleoprotein that is required for the loading of the SMC (structural maintenance of chromosomes) proteins onto the chromosome for chromosomal DNA condensation. Although ParB spreading has been studied, the detailed mechanism is still unclear. In this report, The Helicobacter pylori Spo0J protein (HpSpo0J/ParB) and C-terminal truncated Spo0J protein (residues 1-240) (Ct-HpSpo0J) were expressed and purified. The parS DNA binding ability for Ct-HpSpo0J was determined (Kd= 0.31 ± 0.06 μM). The crystal structure of the Ct-HpSpo0J-parS complex was determined by multi-wavelength anomalous dispersion method at 3.1 Å resolution. Ct-HpSpo0J folds into an elongated structure that includes a flexible N-terminal domain (residues 1-123) for protein-protein interaction and a conserved DNA-binding domain (residues 124-240) for parS binding. Two Ct-HpSpo0J molecules bind with one parS. Ct-HpSpo0J interacts vertically and horizontally with its neighbors through the N-terminal domain to form an oligomer. These adjacent and transverse interactions are accomplished via a highly conserved arginine patch, “RRLR”. From these results, we propose how ParB possibly associates with ParA protein through its protruded N-terminal domains, how ParB spreads along the chromosomal DNA by parS binding, and how ParB bridges DNA to compact and condense the chromosome during chromosome partitioning. Key word: Arginine patch; Chromosome segregation; Helicobacter pylori; ParB spreading