Xu Hongwei, Curtis Tanya Y, Powers Stephen J, Raffan Sarah, Gao Runhong, Huang Jianhua, Heiner Monika, Gilbert David R, Halford Nigel G
Biotechnology Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai, China.
Department of Plant Sciences, Rothamsted Research, Harpenden, United Kingdom.
Front Plant Sci. 2018 Jan 15;8:2237. doi: 10.3389/fpls.2017.02237. eCollection 2017.
Asparagine synthetase activity in cereals has become an important issue with the discovery that free asparagine concentration determines the potential for formation of acrylamide, a probably carcinogenic processing contaminant, in baked cereal products. Asparagine synthetase catalyses the ATP-dependent transfer of the amino group of glutamine to a molecule of aspartate to generate glutamate and asparagine. Here, asparagine synthetase-encoding polymerase chain reaction (PCR) products were amplified from wheat () cv. Spark cDNA. The encoded proteins were assigned the names TaASN1, TaASN2, and TaASN3 on the basis of comparisons with other wheat and cereal asparagine synthetases. Although very similar to each other they differed slightly in size, with molecular masses of 65.49, 65.06, and 66.24 kDa, respectively. Chromosomal positions and scaffold references were established for , and , and a fourth, more recently identified gene, . , and were all found to be single copy genes, located on chromosomes 5, 3, and 4, respectively, of each genome (A, B, and D), although variety Chinese Spring lacked a gene in the B genome. Two copies of were found on chromosome 1 of each genome, and these were given the names and . The TaASN1, TaASN2, and TaASN3 PCR products were heterologously expressed in ( was not investigated in this part of the study). Western blot analysis identified two monoclonal antibodies that recognized the three proteins, but did not distinguish between them, despite being raised to epitopes SKKPRMIEVAAP and GGSNKPGVMNTV in the variable C-terminal regions of the proteins. The heterologously expressed TaASN1 and TaASN2 proteins were found to be active asparagine synthetases, producing asparagine and glutamate from glutamine and aspartate. The asparagine synthetase reaction was modeled using SNOOPY software and information from the BRENDA database to generate differential equations to describe the reaction stages, based on mass action kinetics. Experimental data from the reactions catalyzed by TaASN1 and TaASN2 were entered into the model using Copasi, enabling values to be determined for kinetic parameters. Both the reaction data and the modeling showed that the enzymes continued to produce glutamate even when the synthesis of asparagine had ceased due to a lack of aspartate.
随着发现游离天冬酰胺浓度决定烘焙谷物产品中丙烯酰胺(一种可能致癌的加工污染物)形成的可能性,谷物中天冬酰胺合成酶活性已成为一个重要问题。天冬酰胺合成酶催化谷氨酰胺的氨基以ATP依赖的方式转移到天冬氨酸分子上,生成谷氨酸和天冬酰胺。在此,从小麦()品种Spark的cDNA中扩增出编码天冬酰胺合成酶的聚合酶链反应(PCR)产物。根据与其他小麦和谷物天冬酰胺合成酶的比较,将编码的蛋白质分别命名为TaASN1、TaASN2和TaASN3。尽管它们彼此非常相似,但大小略有不同,分子量分别为65.49、65.06和66.24 kDa。确定了、和以及第四个最近鉴定的基因的染色体位置和支架参考。、和均被发现为单拷贝基因,分别位于每个基因组(A、B和D)的5号、3号和4号染色体上,尽管中国春品种在B基因组中缺少一个基因。在每个基因组的1号染色体上发现了两个拷贝,并将它们命名为和。TaASN1、TaASN2和TaASN3的PCR产物在(本研究的这一部分未对进行研究)中进行了异源表达。蛋白质印迹分析鉴定出两种单克隆抗体,它们能识别这三种蛋白质,但无法区分它们,尽管这两种抗体是针对蛋白质可变C末端区域的表位SKKPRMIEVAAP和GGSNKPGVMNTV制备的。发现异源表达的TaASN1和TaASN2蛋白是有活性的天冬酰胺合成酶,能从谷氨酰胺和天冬氨酸生成天冬酰胺和谷氨酸。使用SNOOPY软件和来自BRENDA数据库的信息对天冬酰胺合成酶反应进行建模,以基于质量作用动力学生成描述反应阶段的微分方程。使用Copasi将TaASN1和TaASN2催化反应的实验数据输入模型,从而能够确定动力学参数的值。反应数据和建模均表明,即使由于天冬氨酸缺乏导致天冬酰胺合成停止,这些酶仍会继续产生谷氨酸。