Activation of the hetero-octameric ATP phosphoribosyl transferase through subunit interface rearrangement by a tRNA synthetase paralog
Activation of the hetero-octameric ATP phosphoribosyl transferase through subunit interface rearrangement by a tRNA synthetase paralog
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DOI：
10.1074/jbc.m505041200
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发表时间：
2005-10-07
影响因子：
4.8
通讯作者：
Francklyn, SS
中科院分区：
文献类型：
--
作者：
Champagne, KS;Sissler, M;Francklyn, SS
ATP磷酸核糖转移酶（ATP-PRT）在启动组氨酸生物合成的高度调节反应中连接ATP和5-磷酸核糖-1-焦磷酸（PRPP）。ATP-PRT的不寻常的异源八聚体形式包括基于周质结合蛋白折叠的四个HisG（S）催化亚基和类似于组氨酰-tRNA合成酶的四个HisZ调节亚基。在这里，我们提出了第一个结构的PRPP结合ATP-PRT在2.9埃，并提供了一个结构模型的基础上，与其他抑制和激活ATP-PRT的异源八聚体和六聚体的家庭比较变构激活。八聚体酶的活化状态的特征在于HisZ-HisG界面中的间质磷酸根离子和HisZ基序2环与HisGS二聚体界面之间的新接触。这些接触重构了界面，以将保守残基募集到活性位点，在那里它们激活焦磷酸盐以促进催化。此外，突变分析鉴定了HisZ和功能性HisRS之间高度保守区域内的组氨酸结合位点。通过与氨酰化和磷酸结合相关的蛋白质结构域的寡聚化和功能重新分配，HisZ-HisG八聚体ATP-PRT获得了以变构调节方式启动关键代谢中间体合成的能力。
ATP phosphoribosyl transferase (ATP-PRT) joins ATP and 5-phosphoribosyl-1- pyrophosphate ( PRPP) in a highly regulated reaction that initiates histidine biosynthesis. The unusual hetero-octameric version of ATP-PRT includes four HisG(S) catalytic subunits based on the periplasmic binding protein fold and four HisZ regulatory subunits that resemble histidyl-tRNA synthetases. Here, we present the first structure of a PRPP-bound ATP-PRT at 2.9 angstrom and provide a structural model for allosteric activation based on comparisons with other inhibited and activated ATP-PRTs from both the hetero-octameric and hexameric families. The activated state of the octameric enzyme is characterized by an interstitial phosphate ion in the HisZ-HisG interface and new contacts between the HisZ motif 2 loop and the HisGS dimer interface. These contacts restructure the interface to recruit conserved residues to the active site, where they activate pyrophosphate to promote catalysis. Additionally, mutational analysis identifies the histidine binding sites within a region highly conserved between HisZ and the functional HisRS. Through the oligomerization and functional re-assignment of protein domains associated with aminoacylation and phosphate binding, the HisZ-HisG octameric ATP-PRT acquired the ability to initiate the synthesis of a key metabolic intermediate in an allosterically regulated fashion.