叶绿体硫氧还蛋白调控谷氨酸-1-半醛氨基转移酶氧化还原状态的研究

The research of glutamate-1-semialdehyde aminotransferase activity regulated by chloroplast thioredoxins in redox

5-氨基乙酰丙酸(5-aminolevulinic acid,ALA)是四吡咯化合物合成的前体分子,它以谷氨酰-tRNA为底物经过一个两步反应形成,分别由谷氨酰-tRNA还原酶(glutamyl-tRNA reductase,GLTR)与谷氨酸-1-半醛氨基转移酶(Glutamate-1-semialdehyde aminotransferase,GSAAT)催化。GSAAT作为调控ALA合成的酶之一,对四吡咯化合物的合成起着至关重要的作用。硫氧还蛋白是一类小分子量的氧化还原蛋白(大约12kD)。它们介导其靶蛋白中半胱氨酸的二硫键与巯基之间的转变从而调控其靶蛋白的功能和稳定性。酵母双杂交试验结果显示,GSAAT与叶绿体硫氧还蛋白F(Thioredoxin-F)发生相互作用。利用VIGS技术沉默豌豆叶片中的叶绿体硫氧还蛋白基因,借助Western Blotting分析体内GSAAT的氧化还原状态,发现叶绿体硫氧还蛋白基因的沉默影响了GSAAT的氧化还原状态。

The first common precursor of all tetrapyrroles, 5-aminolevulinic acid（ALA）, is synthesized from glutamyl-tRNA in a two-step reaction catalyzed by glutamyl-tRNA reductase （GLTR）and glutamate-l-semialdehyde aminotransferase（GSAAT）. The synthesis of 5-amin- olevulinate is the first critical step in tetrapyrroles biosynthesis. Glutamate-l-semialdehyde aminotransferase is one of the enzymes regulating the synthesis of ALA, so it plays a critical role in the process of tetrapyrrole biosynthesis. Thioredoxins are small（approximate 12 kD） redox active proteins and regulate the stability and function of target proteins by mediating the dithiol-disulfide exchange of Cys residues. Through the yeast two-hybrid assay, the result shows GSAAT interact with chloroplast thioredoxin-F. In vivo, using the leaves of VIGS- TRX-F/TRX-M plants, the redox state of GSAAT was analyzed by Western Blotting, andwe found the redox state of GSAAT was regulated by the silence of chloroplast thioredoxins, thus affecting the synthesis of ALA.