Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
J Mol Biol. 2011 Nov 4;413(4):844-56. doi: 10.1016/j.jmb.2011.09.007. Epub 2011 Sep 21.
Phosphoribosyl pyrophosphate (PRPP) synthetase catalyzes the transfer of the pyrophosphate group from ATP to ribose-5-phosphate (R5P) yielding PRPP and AMP. PRPP is an essential metabolite that plays a central role in cellular metabolism. The enzyme from a thermophilic archaeon Thermoplasma volcanium (Tv) was expressed in Escherichia coli, crystallized, and its X-ray molecular structure was determined in a complex with its substrate R5P and with substrate analogs β,γ-methylene ATP and ADP in two monoclinic crystal forms, P2(1). The β,γ-methylene ATP- and the ADP-bound binary structures were determined from crystals grown from ammonium sulfate solutions; these crystals diffracted to 1.8 Å and 1.5 Å resolutions, respectively. Crystals of the ternary complex with ADP-Mg(2+) and R5P were grown from a polyethylene glycol solution in the absence of sulfate ions, and they diffracted to 1.8 Å resolution; the unit cell is approximately double the size of the unit cell of the crystals grown in the presence of sulfate. The Tv PRPP synthetase adopts two conformations, open and closed, at different stages in the catalytic cycle. The binding of substrates, R5P and ATP, occurs with PRPP synthetase in the open conformation, whereas catalysis presumably takes place with PRPP synthetase in the closed conformation. The Tv PRPP synthetase forms a biological dimer in contrast to the tetrameric or hexameric quaternary structures of the Methanocaldococcus jannaschii and Bacillus subtilis PRPP synthetases, respectively.
磷酸核糖焦磷酸（PRPP）合酶催化焦磷酸基团从 ATP 转移到 5-磷酸核糖（R5P），生成 PRPP 和 AMP。PRPP 是一种必需代谢物，在细胞代谢中起着核心作用。来自嗜热古菌 Thermoplasma volcanium（Tv）的酶在大肠杆菌中表达、结晶，并在与其底物 R5P 以及与底物类似物β、γ-亚甲基 ATP 和 ADP 的复合物中确定了其 X 射线分子结构，存在于两种单斜晶系晶体形式 P2(1)中。β、γ-亚甲基 ATP-和 ADP-结合的二元结构是从含有硫酸铵溶液的晶体中确定的；这些晶体分别衍射至 1.8 Å 和 1.5 Å 的分辨率。含有 ADP-Mg(2+)和 R5P 的三元复合物晶体是从不含硫酸盐的聚乙二醇溶液中生长的，其衍射分辨率为 1.8 Å；该晶胞大约是在存在硫酸盐时生长的晶体的两倍大小。Tv PRPP 合酶在催化循环的不同阶段采用开放和封闭两种构象。底物 R5P 和 ATP 的结合发生在 PRPP 合酶的开放构象中，而催化作用可能发生在 PRPP 合酶的封闭构象中。与 Methanocaldococcus jannaschii 和 Bacillus subtilis 的 PRPP 合酶分别形成四聚体或六聚体的四级结构相反，Tv PRPP 合酶形成生物二聚体。
