STRUCTURAL STUDIES OF GUN4 AND THE GUN4/GUN5 COMPLEX

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。叶绿体正常发育所需的许多因子实际上都编码在植物的核基因组中。此外，越来越多的证据表明，这些基因的协调表达在一定程度上取决于叶绿体的功能状态。例如，导致叶绿体发育受阻的核突变也会导致核定位的光合作用基因表达减少。这种来自叶绿体的信号级联对于协调编码光合作用组成部分的核和叶绿体定位基因是必不可少的。拟南芥GUN(基因组解偶联)基因座已被鉴定为叶绿体到细胞核信号通路的组成部分。目前在GUN基因座上有5个已知基因(GUN1、GUN2、GUN3、GUN4和GUN5)，其中GUN5是唯一一个编码具有已知功能的蛋白质的基因，即镁螯合酶的ChlH亚单位。最近发现GUN4编码了一种新的未知功能的蛋白质，它似乎直接与GUN5相互作用，既增强了GUN5的镁螯合酶活性，也增强了它的ATPase活性(未发表的数据RL)。有趣的是，Gun4和Gun5植株的叶绿素积累都减少了，而Gun4gan 5双突变体产生了白化植株。这些发现表明，四吡咯生物合成途径控制编码叶绿体定位蛋白的核基因的转录。为了更好地理解这一信号通路的机制，我们建议对新的蛋白Gun4进行结构表征，并确定Gun4/Gun5介导的镁螯合酶活性背后的生物物理机制。这项工作将为在体外和体内进一步研究这一独特的真核细胞信号转导途径提供模板。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Many of the factors necessary for proper plastid development are actually encoded in the plant's nuclear genome. Furthermore a growing the body of evidence suggests that the coordinated expression of these genes depends in part on the functional state of the chloroplast. For example, nuclear mutations that result in developmentally arrested chloroplasts also result in the reduced expression of nuclear-localized photosynthetic genes. This plastid-derived signaling cascade is essential for coordination of both nuclear and chloroplast localized genes that encode components of photosynthesis. Arabidopsis GUN (genomes uncoupled) loci have been identified as components of the plastid to nucleus signaling pathway. There are currently, five known genes within the GUN loci (GUN1, GUN2, GUN3, GUN4 and GUN5), of which, until recently, GUN5 was the only gene to encode a protein of known function, the ChlH subunit of Mg-chelatase. GUN4 was recently shown to encode a novel protein of unknown function that appears to directly interact with GUN5 to both enhance its Mg-chelatase activity, as well as confer on it, ATPase activity (unpublished data RL). Interestingly, there is a reduction in chlorophyll accumulation in both gun4 and gun5 plants and gun4gun5 double mutants produce albino plants. These findings suggest that the tetrapyrrole biosynthetic pathway controls transcription of nuclear genes encoding plastid-localized proteins. In an effort to understanding the mechanism of this signaling pathway more clearly, we propose to structurally characterize the novel protein gun4 and also determine the biophysical mechanism behind gun4/gun5 mediated Mg-chelatase activity. This work will provide a template for further investigation of this unique signaling pathway both in vitro and in vivo in a model eukaryote, Arabidopsis thaliana.