代谢物在莽草酸途径中的转移
生物谷报道：莽草酸途径是存在于植物、真菌和微生物中的一条重要的代谢途径，该途径有7个酶化过程。脱氢奎尼酸（DHQ）和莽草酸脱氢酶（SDH）促进了莽草酸途径中的第3，4个阶段。在大多数微生物中，DHQ和SDH是单功能的，但是在植物中DHQ和SDH可以融合，形成具有两种功能的酶。DHQ-SDH双功能酶的优点就是在莽草酸途径中通过限制中间物在竞争途径中的质量而增加代谢物流通的效率。
多伦多大学的Christendat小组近日研究分析了拟南芥（一种草本植物）的DHQ-SDH结构。研究人员通过气相悬滴法，第一次完成了DHQ-SDH酶和莽草酸的共结晶，之后将尼克酰胺腺嘌呤二核苷酸磷酸（NADP+）添加到晶体中形成三重复合物。脱氢莽草酸产物在DHQ位点的产生，说明SDH-莽草酸-NADP（H）是一种利于莽草酸氧化的活性复合物，DHQ-SDH的凹型构造中存有活性位点。DHQ-SDH蛋白可以通过面对面定位，将莽草酸途径中的代谢物区分开，而且可增加代谢物从DHQ到SDH域的转移效率。这个模型已经被现有的动力学数据证实，并认为SDH在莽草酸途径中起到存放代谢物的作用。
相关论文发表在《晶体生长与设计》（Crystal Growth & Design）杂志上。（科学新闻杂志 乔莉/编译）
生物谷推荐原始出处：
Cryst. Growth Des.,
Web Release Date: October 23,
The DHQ-dehydroshikimate-SDH-shikimate-NADP(H) Complex: Insights into Metabolite Transfer in the Shikimate Pathway† ,‡
Sasha Anna Singh and
Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Ontario, Canada M5S 3B2
Received July 27, 2007
Abstract:
Revised September 18, 2007Plants encode the bifunctional dehydroquinase-shikimate dehydrogenase (DHQ-SDH), which catalyzes the third and fourth steps of the shikimate pathway. We report the Arabidopsis thaliana DHQ-SDH structure in complex with all of its natural substrates. The DHQ-SDH enzyme was first cocrystallized with shikimate. NADP+ was subsequently added to the crystals yielding the SDH ternary complex. The Pro-R hydrogen of the nicotinamide C4 is 3.35 Å from the C3 of shikimate, the site of hydride transfer. The catalytic Lys 385 and Asp 423 residues are proximal to the C3-hydroxyl of shikimate, which is deprotonated in the oxidation reaction. The SDH-shikimate-NADP(H) complex represents the active complex as the oxidation of shikimate was evidenced by the generation of the product (dehydroshikimate) found in the DHQ site. DHQ-SDH adopts a concave architecture that places the active sites in a face-to-face arrangement. This proximal organization serves to increase the local effective concentration of dehydroshikimate, and as a consequence, reduces the diffusion of the intermediate to the cellular milieu and competing pathways. Our results have also demonstrated the dependence on a number of residues surrounding the C4-hydroxyl group of shikimate for substrate binding and efficient catalysis, including Thr 407, Thr 422, and Gln 578.
- 众说风云 (已有0条评论)
