Park Beom Jun, Yoon Yoo Bin, Park Soon Cheol, Shin Geun-Seup, Kwak Hee-Jin, Lee Dong Ho, Choi Min Young, Kim Jung-Woong, Cho Sung-Jin
Department of Life Science, Chung-Ang University, Seoul 06974, Republic of Korea.
Department of Ecology, Evolution and Behavior, Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
J Invertebr Pathol. 2023 Nov;201:108010. doi: 10.1016/j.jip.2023.108010. Epub 2023 Oct 20.
Toll-like receptors (TLRs), an ancient and well-conserved group of pattern recognition receptors (PRRs), recognize conserved pathogen-associated molecular patterns. TLRs consist of three domains: the extracellular N-terminal domain, containing one or more leucine-rich repeats (LRRs), responsible for the recognizing and binding of antigens; the type-I transmembrane domain; and the intracellular domain known as the Toll/Interleukin-1 receptor (TIR) domain required for the downstream signaling pathway. We identified six new full-length complementary DNA (cDNA) sequences, Ean-TLR1/2/3/4/5/6. The deduced amino acid sequences indicate that Ean-TLRs consist of one signal peptide, one LRR N-terminal domain (Ean-TLR4/5), varying numbers of LRRs, one (Ean-TLR1/2/3/4/5) or two (Ean-TLR6) LRR C-terminal domains, one type-I transmembrane domain, and a TIR domain. In addition, a TIR domain alignment revealed that three conserved motifs, designated as Box 1, Box 2, and Box 3, contain essential amino acid residues for downstream signaling activity. Phylogenetic analysis of earthworm TLRs generated two separate evolutionary branches representing single (sccTLR) and multiple (mccTLR) cysteine cluster TLRs. Ean-TLR1/2/3/4 (sccTLR type) and Ean-TLR6 (mccTLR type) were clustered with corresponding types of previously reported earthworm TLRs as well as TLRs from Clitellata and Polychaete. As PRRs, earthworm TLRs should be capable of sensing a diverse range of pathogens. Except for Ean-TLR3, which was not responsive to any bacteria, earthworm TLR expression was significantly induced by Gram-positive but not Gram-negative bacteria. Moreover, it is likely that earthworms can differentiate between different species of Gram-positive bacteria via their TLR responses. The ligand specificity of earthworm TLRs suggests that their pathogenic ligand recognition is likely to be as specific and diverse as the mammalian TLR pathogen-sensing system.
Toll样受体（TLRs）是一组古老且高度保守的模式识别受体（PRRs），可识别保守的病原体相关分子模式。TLRs由三个结构域组成：细胞外N端结构域，包含一个或多个富含亮氨酸的重复序列（LRRs），负责抗原的识别和结合；I型跨膜结构域；以及细胞内结构域，即下游信号通路所需的Toll/白细胞介素-1受体（TIR）结构域。我们鉴定出六个新的全长互补DNA（cDNA）序列，即Ean-TLR1/2/3/4/5/6。推导的氨基酸序列表明，Ean-TLRs由一个信号肽、一个LRR N端结构域（Ean-TLR4/5）、数量不等的LRRs、一个（Ean-TLR1/2/3/4/5）或两个（Ean-TLR6）LRR C端结构域、一个I型跨膜结构域和一个TIR结构域组成。此外，TIR结构域比对显示，三个保守基序，即Box 1、Box 2和Box 3，包含下游信号传导活性所必需的氨基酸残基。蚯蚓TLRs的系统发育分析产生了两个独立的进化分支，分别代表单个（sccTLR）和多个（mccTLR）半胱氨酸簇TLRs。Ean-TLR1/2/3/4（sccTLR类型）和Ean-TLR6（mccTLR类型）与先前报道的相应类型的蚯蚓TLRs以及来自寡毛纲和多毛纲的TLRs聚集在一起。作为PRRs，蚯蚓TLRs应该能够感知多种病原体。除了对任何细菌均无反应的Ean-TLR3外，革兰氏阳性菌而非革兰氏阴性菌可显著诱导蚯蚓TLR的表达。此外，蚯蚓很可能能够通过其TLR反应区分不同种类的革兰氏阳性菌。蚯蚓TLRs的配体特异性表明，它们对病原体配体的识别可能与哺乳动物TLR病原体传感系统一样特异和多样。
