School of Biosciences, University of Birmingham , Edgbaston, Birmingham B15 2TT, U.K.
ACS Chem Biol. 2013 Oct 18;8(10):2245-55. doi: 10.1021/cb400508k. Epub 2013 Aug 13.
Recent evidence established that the cell envelope of Mycobacterium tuberculosis, the bacillus causing tuberculosis (TB), is coated by an α-glucan-containing capsule that has been implicated in persistence in a mouse infection model. As one of three known metabolic routes to α-glucan in mycobacteria, the cytoplasmic GlgE-pathway converts trehalose to α(1 → 4),α(1 → 6)-linked glucan in 4 steps. Whether individual reaction steps, catalyzed by trehalose synthase TreS, maltokinase Pep2, and glycosyltransferases GlgE and GlgB, occur independently or in a coordinated fashion is not known. Here, we report the crystal structure of M. tuberculosis TreS, and show by small-angle X-ray scattering and analytical ultracentrifugation that TreS forms tetramers in solution. Together with Pep2, TreS forms a hetero-octameric complex, and we demonstrate that complex formation markedly accelerates maltokinase activity of Pep2. Thus, complex formation may act as part of a regulatory mechanism of the GlgE pathway, which overall must avoid accumulation of toxic pathway intermediates, such as maltose-1-phosphate, and optimize the use of scarce nutrients.
最近的证据表明，引起结核病（TB）的分枝杆菌结核分枝杆菌的细胞包膜被含有α-葡聚糖的荚膜覆盖，该荚膜与在小鼠感染模型中的持久性有关。作为分枝杆菌中三种已知的α-葡聚糖代谢途径之一，细胞质 GlgE 途径在 4 步中将海藻糖转化为α(1 → 4)、α(1 → 6)-连接的葡聚糖。由海藻糖合酶 TreS、麦芽糖激酶 Pep2 和糖基转移酶 GlgE 和 GlgB 催化的各个反应步骤是否独立或协调发生尚不清楚。在这里，我们报告了结核分枝杆菌 TreS 的晶体结构，并通过小角度 X 射线散射和分析超速离心表明 TreS 在溶液中形成四聚体。TreS 与 Pep2 形成异八聚体复合物，我们证明复合物形成显着加速了 Pep2 的麦芽糖激酶活性。因此，复合物的形成可能是 GlgE 途径的调节机制的一部分，该机制总体上必须避免有毒途径中间产物（如麦芽糖-1-磷酸）的积累，并优化稀缺营养物质的利用。
