生物谷報道：莽草酸途徑是存在于植物,、真菌和微生物中的一條重要的代謝途徑，該途徑有7個酶化過程,。脫氫奎尼酸（DHQ）和莽草酸脫氫酶（SDH）促進了莽草酸途徑中的第3,，4個階段。在大多數(shù)微生物中,，DHQ和SDH是單功能的,，但是在植物中DHQ和SDH可以融合，形成具有兩種功能的酶,。DHQ-SDH雙功能酶的優(yōu)點就是在莽草酸途徑中通過限制中間物在競爭途徑中的質(zhì)量而增加代謝物流通的效率,。
多倫多大學(xué)的Christendat小組近日研究分析了擬南芥（一種草本植物）的DHQ-SDH結(jié)構(gòu)。研究人員通過氣相懸滴法,，第一次完成了DHQ-SDH酶和莽草酸的共結(jié)晶,，之后將尼克酰胺腺嘌呤二核苷酸磷酸（NADP+）添加到晶體中形成三重復(fù)合物。脫氫莽草酸產(chǎn)物在DHQ位點的產(chǎn)生,，說明SDH-莽草酸-NADP（H）是一種利于莽草酸氧化的活性復(fù)合物,，DHQ-SDH的凹型構(gòu)造中存有活性位點,。DHQ-SDH蛋白可以通過面對面定位，將莽草酸途徑中的代謝物區(qū)分開,，而且可增加代謝物從DHQ到SDH域的轉(zhuǎn)移效率,。這個模型已經(jīng)被現(xiàn)有的動力學(xué)數(shù)據(jù)證實，并認(rèn)為SDH在莽草酸途徑中起到存放代謝物的作用,。
相關(guān)論文發(fā)表在《晶體生長與設(shè)計》（Crystal Growth & Design）雜志上,。（科學(xué)新聞雜志 喬莉/編譯）
生物谷推薦原始出處：
Cryst. Growth Des., 7 (11), 2153–2160 10.1021/cg7007107
Web Release Date: October 23, 2007 Copyright © 2007 American Chemical Society
The DHQ-dehydroshikimate-SDH-shikimate-NADP(H) Complex: Insights into Metabolite Transfer in the Shikimate Pathway† ,‡
Sasha Anna Singh and Dinesh Christendat*
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.
