Mougous Joseph D, Lee Dong H, Hubbard Sarah C, Schelle Michael W, Vocadlo David J, Berger James M, Bertozzi Carolyn R
Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, California 94720, USA.
Mol Cell. 2006 Jan 6;21(1):109-22. doi: 10.1016/j.molcel.2005.10.034.
Sulfate assimilation is a critical component of both primary and secondary metabolism. An essential step in this pathway is the activation of sulfate through adenylation by the enzyme ATP sulfurylase (ATPS), forming adenosine 5'-phosphosulfate (APS). Proteobacterial ATPS overcomes this energetically unfavorable reaction by associating with a regulatory G protein, coupling the energy of GTP hydrolysis to APS formation. To discover the molecular basis of this unusual role for a G protein, we biochemically characterized and solved the X-ray crystal structure of a complex between Pseudomonas syringae ATPS (CysD) and its associated regulatory G protein (CysN). The structure of CysN*D shows the two proteins in tight association; however, the nucleotides bound to each subunit are spatially segregated. We provide evidence that conserved switch motifs in the G domain of CysN allosterically mediate interactions between the nucleotide binding sites. This structure suggests a molecular mechanism by which conserved G domain architecture is used to energetically link GTP turnover to the production of an essential metabolite.
硫酸盐同化是初级和次级代谢的关键组成部分。该途径中的一个关键步骤是通过ATP硫酸化酶（ATPS）的腺苷化作用激活硫酸盐，形成腺苷5'-磷酸硫酸酯（APS）。变形菌门的ATPS通过与一种调节性G蛋白结合，将GTP水解的能量与APS形成相偶联，从而克服了这个能量上不利的反应。为了揭示G蛋白这一特殊作用的分子基础，我们对丁香假单胞菌ATPS（CysD）与其相关调节性G蛋白（CysN）之间的复合物进行了生化表征并解析了其X射线晶体结构。CysN*D的结构显示这两种蛋白质紧密结合；然而，结合在每个亚基上的核苷酸在空间上是分离的。我们提供的证据表明，CysN的G结构域中保守的开关基序通过变构作用介导核苷酸结合位点之间的相互作用。该结构提示了一种分子机制，即利用保守的G结构域架构在能量上把GTP周转与一种必需代谢物的产生联系起来。
