Spo0J (孢子形成零階段蛋白J，屬於ParB家族) 是ParABS (染色體分離系統:ParA，ParB 及parS)的一個重要組成蛋白與細菌的染色體分離有關。ParB (分離蛋白B)與其調節蛋白，ParA (分離蛋白A)與parS DNA交互作用促進染色體的分離。ParB結合染色體上特定parS DNA以及相鄰的非專一性DNA。各個ParB分子可以聚集在一起並沿著染色體傳播與擴散。ParB多聚合物和parS交互作用後所形成的高階核蛋白(high order nucleoprotein)集結染色體結構維持蛋白(SMC)的複合物並組裝到染色體上，藉此使染色體DNA凝聚，以便繼續進行染色體的分離及分配。ParB 傳播與擴散的功能雖然陸續有相關的文獻報導，但是詳細的功能機制尚未清楚。
胃幽門螺旋桿菌Spo0J蛋白 (HpSpo0J/ParB) 及氨基端片斷(#1-240 殘基) Spo0J (Ct-HpSpo0J)蛋白成功表達與純化。Ct-HpSpo0J的parS結合能力被決定，其解離常數為0.31 ± 0.06微莫耳濃度。其Ct-HpSpo0J-parS結構是我們利用多波長異常色散方法解析，解析度為3.1埃。Ct-HpSpo0J的分子結構折疊為一長型的分子形狀，包括具有蛋白分子間交互作用之氨基端功能域(#1-123殘基)及具有parS結合功能之DNA結合功能域(#124-240 殘基)。兩個Ct-HpSpo0J分子與parS結合。此外，Ct-HpSpo0J分子利用其氨基端功能域進行垂直和水平方向之交互作用來形成寡聚合物。這些相鄰及對向的相互作用是藉由一段高度保留之精氨酸序列 “RRLR” 來進行。這些相互作用可能與高階核蛋白複合分子的組裝及ParB傳播與擴散機制有關聯。我們的實驗結果提出在形成高階核蛋白複合體時，ParB是如何利用氨基端功能域和ParA進行交互作用，以及ParB是如何利用和parS的結合使其沿著染色體進行傳播的動作。我們提出一個ParB傳播與擴散模型去解釋染色體DNA分配時期，ParB是如何利用分子架橋的方式讓DNA凝聚並形成具功能性的高階複合物將染色體準確的分配到兩個子細胞中。

關鍵字: 精氨酸序列;染色體分離;胃幽門螺旋桿菌;ParB 傳播

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

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