Nazarian Firouzabadi Farhad, Vincken Jean-Paul, Ji Qin, Suurs Luc C J M, Visser Richard G F
Graduate School Experimental Plant Sciences, Laboratory of Plant Breeding, Wageningen University, PO Box 386, 6700 AJ Wageningen, the Netherlands.
Plant Biotechnol J. 2007 Jan;5(1):134-45. doi: 10.1111/j.1467-7652.2006.00227.x.
Starch is used in many industrial applications, but often requires chemical derivatization to enhance its properties before use. In particular, the stability of starch polymers in solution is improved by acetylation. A drawback of this treatment is the use of pollutant chemicals. A biological alternative to chemical derivatization was investigated by the expression of an amyloplast-targeted Escherichia coli maltose acetyltransferase (MAT) gene in tubers of wild-type (Kardal) and mutant amylose-free (amf) potato plants. MAT was expressed as such, or fused to the N- or C-terminus of a non-catalytic starch-binding domain (SBD) to target the starch granule. Starch granules derived from transgenic plants were found to contain acetyl groups, although their content was low, opening up an avenue to move away from the post-harvest chemical derivatization of starch. MAT inside starch granules was found to be active post-harvest when supplied with acetyl-coenzyme A and glucose or maltose, but it did not acetylate starch polymers in vitro. Starch granules from transformants in which MAT alone was expressed also showed MAT activity, indicating that MAT is accumulated in starch granules, and has affinity for starch by itself. Furthermore, starch granule morphology was altered, and fusion proteins containing MAT and SBD seemed to have a higher affinity for starch granules than two appended SBDs. These results are discussed against the background of the quaternary structure of MAT.
淀粉在许多工业应用中都有使用，但在使用前通常需要进行化学衍生化以增强其性能。特别是，通过乙酰化可以提高淀粉聚合物在溶液中的稳定性。这种处理方法的一个缺点是使用了污染性化学物质。通过在野生型（卡尔达尔）和无直链淀粉突变体（amf）马铃薯植株的块茎中表达定位于造粉体的大肠杆菌麦芽糖乙酰转移酶（MAT）基因，研究了一种化学衍生化的生物替代方法。MAT以这种形式表达，或者与非催化淀粉结合结构域（SBD）的N端或C端融合以靶向淀粉颗粒。发现来自转基因植物的淀粉颗粒含有乙酰基，尽管其含量较低，这为摆脱淀粉收获后的化学衍生化开辟了一条途径。当提供乙酰辅酶A和葡萄糖或麦芽糖时，发现淀粉颗粒内的MAT在收获后具有活性，但它在体外不会使淀粉聚合物乙酰化。仅表达MAT的转化体的淀粉颗粒也显示出MAT活性，这表明MAT积累在淀粉颗粒中，并且自身对淀粉具有亲和力。此外，淀粉颗粒形态发生了改变，含有MAT和SBD的融合蛋白似乎比两个附加的SBD对淀粉颗粒具有更高的亲和力。这些结果是在MAT四级结构的背景下进行讨论的。
