10月5日，J. Biol. Chem.在线发表了生化与细胞所王恩多研究组研究论文：血红素结合人细胞质精氨酰-tRNA合成酶并抑制其催化活力。
人细胞质精氨酰-tRNA合成酶(hcArgRS)催化tRNAArg氨基酰化生成Arg-tRNAArg。Arg-tRNAArg一方面是蛋白质生物合成的原料，参与蛋白质合成；另一方面它也是精氨酰-tRNA：蛋白质转移酶的底物，转移精氨酰基到蛋白质的N-末端，参与依赖泛素化的“N-末端规则”蛋白质降解途径。哺乳动物细胞的ArgRS即参与蛋白质生物合成，又参与蛋白质的降解，如何调节ArgRS的这两个相反的功能是非常重要的科学问题。血红素作为信号分子，参与到许多重要的生命活动中，其中“N-末端规则”途径就是一个血红素的感应器。
王恩多实验室的杨芳博士研究了血红素与hcArgRS在体外的相互作用，研究结果表明血红素能够以hcArgRS的Cys-115 作为特异性的轴向配体与之结合，血红素通过抑制hcArgRS的第一步反应—氨基酸活化反应，而抑制酶的tRNA精氨酰化活力。血红素诱导hcArgRS的寡聚化是其抑制该酶催化活力的主要原因。氨基酰-tRNA合成酶家族是一个功能多样的蛋白质家族，该研究对进一步深入探索哺乳动物ArgRS新的生物学功能提供了极有价值的线索。
该研究工作得到科技部重大科学研究计划，中国博士后基金，上海市博士后基金，中科院王宽诚博士后基金以及上海生科院博士后基金的经费资助。(生物谷Bioon.com)
生物谷推荐英文摘要：
JBC doi: 10.1074/jbc.M110.159913
Hemin binds to human cytoplasmic arginyl-tRNA synthetase and inhibits its catalytic activity
Fang Yang, Xian Xia, Hui-Yan Lei and En-Duo Wang*
The free form of human cytoplasmic arginyl-tRNA synthetase (hcArgRS) is hypothesized to participate in ubiquitin-dependent protein degradation by offering arginyl-tRNAArg to arginyl-tRNA transferase (ATE1). We investigated the effect of hemin on hcArgRS based on the fact that hemin regulates several critical proteins in "N-end rule"protein degradation pathway. Extensive biochemical evidence has established that hemin could bind to both forms of hcArgRS in vitro. Based on the spectral changes of the Soret band on site-directed protein mutants, we identified Cys-115 as a specific axial ligand of hemin binding that is located in the Add1 domain. Hemin inhibited the catalytic activity of full-length and N-terminal 72-amino acid truncated hcArgRSs by blocking amino acid activation. Kinetic analysis demonstrated that the Km values for tRNAArg, arginine and ATP in the presence of hemin were not altered, but kcat values dramatically decreased compared with those in the absence of hemin. By comparison, the activity of prokaryotic ArgRS was not affected obviously by hemin. Gel filtration chromatography suggested that hemin induced oligomerization of both the isolated Add1 domain and the wild type enzyme, which could account for the inhibition of catalytic activity. However, the catalytic activity of a hcArgRS mutant with Cys-115 replaced by alanine (hcArgRS-C115A) was also inhibited by hemin, suggesting that hemin binding to Cys-115 is not responsible for the inhibition of enzymatic activity and that the specific binding may participate in other biological functions.
