JBC：关键蛋白AAA结构域的新作用机制

　　

生物通报道：来自同济大学生命科学与技术学院，南开大学的研究人员发表了题为“Structural insights into unusually strong ATPase activity of the AAA domain of C. elegans fidgetin like-1 protein”的文章，阐明了线虫源Fidgetin like-1蛋白AAA结构域具有高ATPase活性的结构机制。这一研究成果公布在The Journal of Biological Chemistry (JBC) 杂志上。

Fidgetin蛋白是小鼠自发突变种fidget中的突变基因所编码的一个AAA（ATPase associated with various cellular activities）蛋白。因为fidget小鼠呈现多种发育异常，如多趾、小眼、内耳半规管缺失等表型，所以推测fidgetin蛋白参与了这些发育过程，但是该蛋白具体的生化活性和生物学功能却一直不清楚。

在这篇文章中，研究人员首先重组表达了线虫fidgetin同源蛋白fidgetin like-1的AAA结构域（CeFIGL-1-AAA)，意外地发现它具有很高的ATPase活性和寡聚化能力。在解析了晶体结构之后发现，该蛋白在亚基之间会形成特有的静电相互作用；把参与该作用的氨基酸残基突变之后就会显著降低该蛋白的ATPase活性和寡聚化能力。

这些独特的性质说明线虫源fidgetin like-1蛋白可能具有与其它同源蛋白所不同的生物学功能，这为fidgetin蛋白的活性和功能研究提供了重要线索。

Fidgetin是2000年发现的一个AAA蛋白家族新成员，同源序列分析表明它与ka-tanin、spastin属于AAA家族的同一亚家族，因此可能也具有ATP依赖的微管切割活性，ATP的结合和水解应该发生于fidgetin蛋白中保守的AAA结构域。

此前同济大学研究组曾在大肠杆菌中重组表达的人源fidgetin like-1(FIGL-1)蛋白的AAA结构域片段(HsFIGL-1-AAA)，研究人员发现与其他AAA蛋白的序列比对，Sensor 2 motif中保守的Arg残基在HsFIGL-1-AAA结构域中为Thr，但该位点的突变T609R并未明显改变该蛋白的ATPase活性。这些结果提示HsFIGL-1可能以一种特殊的方式发挥功能。

（生物通：万纹）

原文摘要：

Structural insights into unusually strong ATPase activity of the AAA domain of C. elegans fidgetin like-1 protein.

Fidgetin like-1 protein (FIGL-1) is a homolog of fidgetin, a protein whose mutation leads to multiple developmental defects. FIGL-1 protein contains an AAA (ATPase associated with various activities) domain, and belongs to the AAA superfamily. However, the biological functions and developmental implications of this protein remain unknown. Here, we show that the AAA domain of the C. elegans FIGL-1 protein (CeFIGL-1-AAA), in clear contrast to homologous AAA domains, has an unusually high ATPase activity and forms a hexamer in solution. By determining the crystal structure of CeFIGL-1-AAA, we found that the loop linking helices α9 and α10 folds into a short helix α9a, which has an acidic surface and interacts with a positively-charged surface of neighboring subunit. Disruption of this charge interaction by mutagenesis diminishes both the ATPase activity and the oligomerization capacity of the protein. Interestingly, the acidic residues in α9a of CeFIGL-1-AAA are not conserved in other homologous AAA domains that have relatively low ATPase activities. These results demonstrate that the sequence of CeFIGL-1-AAA has adapted to establish an intersubunit charge interaction, which contributes to its strong oligomerization and ATPase activity. These unique properties of CeFIGL-1-AAA distinguish it from other homologous proteins, suggesting that CeFIGL-1 may have a distinct biological function.