Yamamoto Kosuke, Oguri Suguru, Momonoki Yoshie S
Faculty of Bioindustry, Tokyo University of Agriculture, 196 Yasaka, Abashiri, Hokkaido 099-2493, Japan.
Planta. 2008 Mar;227(4):809-22. doi: 10.1007/s00425-007-0658-0. Epub 2007 Nov 28.
We recently identified plant acetylcholinesterases (E.C.3.1.1.7; AChEs) homologous to the AChE purified from a monocotyledon, maize, that are distinct from the animal AChE family. In this study, we purified, cloned and characterized an AChE from a dicotyledon, siratro. The full-length cDNA of siratro AChE is 1,441 nucleotides, encoding a 382-residue protein that includes a signal peptide. This AChE is a disulfide-linked 125-kDa homotrimer consisting of 41-42 kDa subunits, in contrast to the maize AChE, which exists as a mixture of disulfide and non-covalently linked 88-kDa homodimers. The plant AChEs apparently consist of various quaternary structures, depending on the plant species, similar to the animal AChEs. We compared the enzymatic properties of the dimeric maize and trimeric siratro AChEs. Similar to electric eel AChE, both plant AChEs hydrolyzed acetylthiocholine (or acetylcholine) and propionylthiocholine (or propionylcholine), but not butyrylthiocholine (or butyrylcholine), and their specificity constant was highest against acetylcholine. There was no significant difference between the enzymatic properties of trimeric and dimeric AChEs, although two plant AChEs had low substrate turnover numbers compared with electric eel AChE. The two plant AChE activities were not inhibited by excess substrate concentrations. Thus, similar to some plant AChEs, siratro and maize AChEs showed enzymatic properties of both animal AChE and animal BChE. On the other hand, both siratro and maize AChEs exhibited low sensitivity to the AChE-specific inhibitor neostigmine bromide, dissimilar to other plant AChEs. These differences in enzymatic properties of plant AChEs may reflect the phylogenetic evolution of AChEs.
我们最近鉴定出了与从单子叶植物玉米中纯化得到的乙酰胆碱酯酶（E.C.3.1.1.7；AChEs）同源的植物乙酰胆碱酯酶，它们不同于动物AChE家族。在本研究中，我们从双子叶植物南美蟛蜞菊中纯化、克隆并表征了一种AChE。南美蟛蜞菊AChE的全长cDNA为1441个核苷酸，编码一个包含信号肽的382个残基的蛋白质。这种AChE是一种由41 - 42 kDa亚基组成的二硫键连接的125 kDa同三聚体，而玉米AChE则以二硫键连接和非共价连接的88 kDa同二聚体的混合物形式存在。与动物AChEs类似，植物AChEs显然由各种四级结构组成，这取决于植物物种。我们比较了二聚体玉米AChE和三聚体南美蟛蜞菊AChE的酶学性质。与电鳗AChE类似，这两种植物AChEs都能水解乙酰硫代胆碱（或乙酰胆碱）和丙酰硫代胆碱（或丙酰胆碱），但不能水解丁酰硫代胆碱（或丁酰胆碱），并且它们对乙酰胆碱的特异性常数最高。三聚体和二聚体AChEs的酶学性质之间没有显著差异，尽管与电鳗AChE相比，这两种植物AChEs的底物周转率较低。这两种植物AChE活性不受过量底物浓度的抑制。因此，与一些植物AChEs类似，南美蟛蜞菊和玉米AChEs表现出动物AChE和动物BChE的酶学性质。另一方面，南美蟛蜞菊和玉米AChEs对AChE特异性抑制剂溴新斯的明的敏感性较低，这与其他植物AChEs不同。植物AChEs这些酶学性质的差异可能反映了AChEs的系统发育进化。
