Bamming Darja, Horvath Curt M
Department of Biochemistry, Molecular Biology, and Cell Biology and Department of Medicine, Northwestern University, USA.
J Biol Chem. 2009 Apr 10;284(15):9700-12. doi: 10.1074/jbc.M807365200. Epub 2009 Feb 11.
Intracellular pattern recognition receptors MDA5, RIG-I, and LGP2 are essential components of the cellular response to virus infection and are homologous to the DEXH box subfamily of RNA helicases. However, the relevance of helicase activity in the regulation of interferon production remains elusive. To examine the importance of the helicase domain function for these signaling proteins, a series of mutations targeting conserved helicase sequence motifs were analyzed for enzymatic activity, RNA binding, interferon induction, and antiviral signaling. Results indicate that all targeted motifs are required for ATP hydrolysis, but a subset is involved in RNA binding. The enzymatically inactive mutants differed in their signaling ability. Notably, mutations to MDA5 motifs I, III, and VI and RIG-I motif III produced helicase proteins with constitutive antiviral activity, whereas mutations in RIG-I motif V retained ATP hydrolysis but failed to mediate signal transduction. These findings demonstrate that type I interferon production mediated by full-length MDA5 and RIG-I is independent of the helicase domain catalytic activity. In addition, neither enzymatic activity nor RNA binding was required for negative regulation of antiviral signaling by LGP2, supporting an RNA-independent interference mechanism.
细胞内模式识别受体MDA5、RIG-I和LGP2是细胞对病毒感染反应的重要组成部分，与RNA解旋酶的DEXH盒亚家族同源。然而，解旋酶活性在干扰素产生调节中的相关性仍不明确。为了研究解旋酶结构域功能对这些信号蛋白的重要性，分析了一系列针对保守解旋酶序列基序的突变体的酶活性、RNA结合、干扰素诱导和抗病毒信号传导。结果表明，所有靶向基序都是ATP水解所必需的，但其中一部分参与RNA结合。酶活性失活的突变体在信号传导能力上有所不同。值得注意的是，MDA5基序I、III和VI以及RIG-I基序III的突变产生了具有组成型抗病毒活性的解旋酶蛋白，而RIG-I基序V的突变保留了ATP水解能力，但未能介导信号转导。这些发现表明，全长MDA5和RIG-I介导的I型干扰素产生独立于解旋酶结构域的催化活性。此外，LGP2对抗病毒信号的负调节既不需要酶活性也不需要RNA结合，这支持了一种不依赖RNA的干扰机制。
