Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, Japan.
Mol Biol Evol. 2013 Jan;30(1):167-76. doi: 10.1093/molbev/mss213. Epub 2012 Aug 30.
Innate immunity in corals is of special interest not only in the context of self-defense but also in relation to the establishment and collapse of their obligate symbiosis with dinoflagellates of the genus Symbiodinium. In innate immunity system of vertebrates, approximately 20 tripartite nucleotide oligomerization domain (NOD)-like receptor proteins that are defined by the presence of a NAIP, CIIA, HET-E and TP1 (NACHT) domain, a C-terminal leucine-rich repeat (LRR) domain, and one of three types of N-terminal effector domain, are known to function as the primary intracellular pattern recognition molecules. Surveying the coral genome revealed not only a larger number of NACHT- and related domain nucleotide-binding adaptor shared by APAF-1, R proteins, and CED-4 (NB-ARC)-encoding loci (~500) than in other metazoans but also surprising diversity of domain combinations among the coral NACHT/NB-ARC-containing proteins; N-terminal effector domains included the apoptosis-related domains caspase recruitment domain (CARD), death effector domain (DED), and Death, and C-terminal repeat domains included LRRs, tetratricopeptide repeats, ankyrin repeats, and WD40 repeats. Many of the predicted coral proteins that contain a NACHT/NB-ARC domain also contain a glycosyl transferase group 1 domain, a novel domain combination first found in metazoans. Phylogenetic analyses suggest that the NACHT/NB-ARC domain inventories of various metazoan lineages, including corals, are largely products of lineage-specific expansions. Many of the NACHT/NB-ARC loci are organized in pairs or triplets in the Acropora genome, suggesting that the large coral NACHT/NB-ARC repertoire has been generated at least in part by tandem duplication. In addition, shuffling of N-terminal effector domains may have occurred after expansions of specific NACHT/NB-ARC-repeat domain types. These results illustrate the extraordinary complexity of the innate immune repertoire of corals, which may in part reflect adaptive evolution to a symbiotic lifestyle in a uniquely complex and challenging environment.
珊瑚的先天免疫系统不仅在自我防御方面具有特殊意义，而且与它们与共生鞭毛藻属的共生关系的建立和崩溃有关。在脊椎动物的先天免疫系统中，大约有 20 种三部分核苷酸寡聚化结构域（NOD）样受体蛋白，这些蛋白的特征是存在一个 NAIP、CIIA、HET-E 和 TP1（NACHT）结构域、一个 C 端富含亮氨酸重复（LRR）结构域和三种类型的 N 端效应结构域之一，被认为是主要的细胞内模式识别分子。对珊瑚基因组的调查不仅揭示了比其他后生动物更多的 NACHT 和相关结构域核苷酸结合适配器，这些适配器由 APAF-1、R 蛋白和 CED-4（NB-ARC）编码基因共享（~500 个），而且珊瑚 NACHT/NB-ARC 含有的蛋白质中存在令人惊讶的结构域组合多样性；N 端效应结构域包括凋亡相关结构域半胱氨酸天冬氨酸蛋白酶募集结构域（CARD）、死亡效应结构域（DED）和死亡结构域，C 端重复结构域包括 LRRs、四肽重复、锚蛋白重复和 WD40 重复。许多含有 NACHT/NB-ARC 结构域的预测珊瑚蛋白还含有糖基转移酶组 1 结构域，这是首次在后生动物中发现的一种新型结构域组合。系统发育分析表明，各种后生动物谱系（包括珊瑚）的 NACHT/NB-ARC 结构域库存主要是谱系特异性扩张的产物。在 Acropora 基因组中，许多 NACHT/NB-ARC 基因座以对或三联体的形式组织，这表明珊瑚的大型 NACHT/NB-ARC 库至少部分是通过串联重复产生的。此外，在特定的 NACHT/NB-ARC-重复结构域类型的扩张之后，N 端效应结构域的重排可能已经发生。这些结果说明了珊瑚先天免疫系统的非凡复杂性，这在一定程度上反映了对共生生活方式的适应性进化，这种生活方式存在于一个独特复杂和具有挑战性的环境中。
