Wu Baojun, Huan Tianxiao, Gong Jing, Zhou Pin, Bai Zengliang
Laboratory of Developmental Immunology, School of Life Science, Shandong University, Jinan 250100, People's Republic of China.
J Genet. 2011 Dec;90(3):401-8. doi: 10.1007/s12041-011-0097-3.
Domain shuffling, which is an important mechanism in the evolution of multi-domain proteins, has shaped the evolutionary development of the immune system in animals. Toll and Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate and adaptive immune systems. Draft genome sequences provide the opportunity to compare the Toll/TLR gene repertoire among representative metazoans. In this study, we investigated the combination of Toll/interleukin-1 receptor (TIR) and leucine-rich repeat (LRR) domains of metazoan Toll/TLRs. Before Toll with both domains occurred in Cnidaria (sea anemone, Nematostella vectensis), through domain combinations, TIR-only and LRR-only proteins had already appeared in sponges (Amphimedon queenslandica). Although vertebrate-like TIR (V-TIR) domain already appeared in Cnidaria, the vertebrate-like TLR (V-TLR) with both domains appeared much later. The first combination between V-TIR domain and vertebrate-like LRR (V-LRR) domain for V-TLR may have occurred after the divergence of Cnidaria and bilateria. Then, another combination for V-TLR, a recombination of both domains, possibly occurred before or during the evolution of primitive vertebrates. Taken together, two rounds of domain combinations may thus have co-shaped the vertebrate TLRs.
结构域洗牌是多结构域蛋白质进化中的一种重要机制，它塑造了动物免疫系统的进化发展。Toll及Toll样受体（TLR）是一类在先天性和适应性免疫系统中起关键作用的蛋白质。基因组草图序列提供了比较代表性后生动物中Toll/TLR基因库的机会。在本研究中，我们调查了后生动物Toll/TLR的Toll/白细胞介素-1受体（TIR）结构域和富含亮氨酸重复序列（LRR）结构域的组合情况。在刺胞动物（海葵，星状海葵）中出现同时具有这两个结构域的Toll之前，通过结构域组合，仅含TIR的蛋白和仅含LRR的蛋白已在海绵动物（昆士兰扁海绵）中出现。虽然类似脊椎动物的TIR（V-TIR）结构域在刺胞动物中已经出现，但同时具有这两个结构域的类似脊椎动物的TLR（V-TLR）出现得要晚得多。V-TLR的V-TIR结构域与类似脊椎动物的LRR（V-LRR）结构域的首次组合可能发生在刺胞动物和两侧对称动物分化之后。然后，V-TLR的另一种组合，即两个结构域的重组，可能发生在原始脊椎动物进化之前或期间。综上所述，两轮结构域组合可能共同塑造了脊椎动物的TLR。
