近日，美國(guó)兩所大學(xué)的研究人員在植物細(xì)胞壁形成問(wèn)題上有了新的突破,，這一新發(fā)現(xiàn)為擴(kuò)大可再生能源的原料鋪平道路。
研究人員確認(rèn)了兩種蛋白質(zhì),，GAUT1和GAUT7共同形成了植物細(xì)胞壁中的果膠,。果膠是一種多糖，對(duì)植物的生長(zhǎng)發(fā)育是至關(guān)重要的,，它也常作為凝膠劑用于果醬和果凍生產(chǎn)中,。該發(fā)現(xiàn)為使用植物細(xì)胞壁形成的可再生生物質(zhì)能奠定了基礎(chǔ)。植物細(xì)胞壁原料可以作為一種碳?xì)浠衔镉糜谏a(chǎn)乙醇,，但是由于很難分解復(fù)雜的植物細(xì)胞壁,，因此難以獲得足夠的能源。美國(guó)政府現(xiàn)在大力推行從植物細(xì)胞壁中生產(chǎn)生物能源,。目前美國(guó)大部分的乙醇是從玉米淀粉中獲得的,，但是政府一直都在找尋其他可再生能源原料，將不會(huì)與國(guó)家糧食供應(yīng)競(jìng)爭(zhēng),。有關(guān)果膠是如何形成細(xì)胞壁的這一新認(rèn)知,，可以幫助研究人員通過(guò)使用轉(zhuǎn)基因植物來(lái)生產(chǎn)更多的乙醇。如果了解了細(xì)胞壁的組成,，人們就可以改變生物合成酶,，使得細(xì)胞壁更容易被分解，這樣可以更具成本效益的生產(chǎn)生物乙醇或其他生物燃料,。
研究人員發(fā)現(xiàn)GAUT7把GAUT1錨定在植物細(xì)胞的高爾基體中,，這是第一次在高爾基體的蛋白質(zhì)中發(fā)現(xiàn)錨定機(jī)制。這是一項(xiàng)重要的發(fā)現(xiàn),，研究人員認(rèn)為它可能代表一個(gè)范式,，即一種蛋白質(zhì)可以錨定催化亞基。使用相同的機(jī)制也許還可以發(fā)現(xiàn)其他的化合物,。
科學(xué)家通常側(cè)重于研究植物細(xì)胞壁的其他組成部分,，如纖維素，但這項(xiàng)研究則是研究果膠,，但果膠的結(jié)構(gòu)比纖維素結(jié)構(gòu)更為復(fù)雜,。下一步研究人員想要了解在果膠形成過(guò)程中，其他蛋白質(zhì)是如何與化合物關(guān)聯(lián)的,，以及之間的相互作用,，并確認(rèn)GAUT7的哪一部分起到了粘接作用。這樣將有助于研究人員修改細(xì)胞壁合成以生產(chǎn)可再生能源,。 （生物谷Bioon.com）
doi:10.1073/pnas.1112816108
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Galacturonosyltransferase (GAUT)1 and GAUT7 are the core of a plant cell wall pectin biosynthetic homogalacturonan:galacturonosyltransferase complexMelani A. Atmodjo, Yumiko Sakuragi, Xiang Zhu, Amy J. Burrell, Sushree S. Mohanty, James A. Atwood III, Ron Orlando, Henrik V. Scheller, and Debra MohnenPlant cell wall pectic polysaccharides are arguably the most complex carbohydrates in nature. Progress in understanding pectin synthesis has been slow due to its complex structure and difficulties in purifying and expressing the low-abundance, Golgi membrane-bound pectin biosynthetic enzymes. Arabidopsis galacturonosyltransferase (GAUT) 1 is an α-1,4-galacturonosyltransferase (GalAT) that synthesizes homogalacturonan (HG), the most abundant pectic polysaccharide. We now show that GAUT1 functions in a protein complex with the homologous GAUT7. Surprisingly, although both GAUT1 and GAUT7 are type II membrane proteins with single N-terminal transmembrane-spanning domains, the N-terminal region of GAUT1, including the transmembrane domain, is cleaved in vivo. This raises the question of how the processed GAUT1 is retained in the Golgi, the site of HG biosynthesis. We show that the anchoring of GAUT1 in the Golgi requires association with GAUT7 to form the GAUT1:GAUT7 complex. Proteomics analyses also identified 12 additional proteins that immunoprecipitate with the GAUT1:GAUT7 complex. This study provides conclusive evidence that the GAUT1:GAUT7 complex is the catalytic core of an HG:GalAT complex and that cell wall matrix polysaccharide biosynthesis occurs via protein complexes. The processing of GAUT1 to remove its N-terminal transmembrane domain and its anchoring in the Golgi by association with GAUT7 provides an example of how specific catalytic domains of plant cell wall biosynthetic glycosyltransferases could be assembled into protein complexes to enable the synthesis of the complex and developmentally and environmentally plastic plant cell wall.
