Voogdt Carlos G P, Bouwman Lieneke I, Kik Marja J L, Wagenaar Jaap A, van Putten Jos P M
Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL, Utrecht, the Netherlands.
Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL, Utrecht, the Netherlands.
Sci Rep. 2016 Jan 7;6:19046. doi: 10.1038/srep19046.
Toll-like receptors (TLR) are ancient innate immune receptors crucial for immune homeostasis and protection against infection. TLRs are present in mammals, birds, amphibians and fish but have not been functionally characterized in reptiles despite the central position of this animal class in vertebrate evolution. Here we report the cloning, characterization, and function of TLR5 of the reptile Anolis carolinensis (Green Anole lizard). The receptor (acTLR5) displays the typical TLR protein architecture with 22 extracellular leucine rich repeats flanked by a N- and C-terminal leucine rich repeat domain, a membrane-spanning region, and an intracellular TIR domain. The receptor is phylogenetically most similar to TLR5 of birds and most distant to fish TLR5. Transcript analysis revealed acTLR5 expression in multiple lizard tissues. Stimulation of acTLR5 with TLR ligands demonstrated unique responsiveness towards bacterial flagellin in both reptile and human cells. Comparison of acTLR5 and human TLR5 using purified flagellins revealed differential sensitivity to Pseudomonas but not Salmonella flagellin, indicating development of species-specific flagellin recognition during the divergent evolution of mammals and reptiles. Our discovery of reptile TLR5 fills the evolutionary gap regarding TLR conservation across vertebrates and provides novel insights in functional evolution of host-microbe interactions.
Toll样受体（TLR）是古老的天然免疫受体，对免疫稳态和抗感染至关重要。TLR存在于哺乳动物、鸟类、两栖动物和鱼类中，但在爬行动物中尚未进行功能表征，尽管该动物类群在脊椎动物进化中处于核心地位。在此，我们报告了爬行动物绿安乐蜥（Anolis carolinensis）TLR5的克隆、表征及功能。该受体（acTLR5）具有典型的TLR蛋白结构，有22个细胞外富含亮氨酸重复序列，两侧分别为N端和C端富含亮氨酸重复结构域、跨膜区和细胞内TIR结构域。该受体在系统发育上与鸟类的TLR5最相似，与鱼类的TLR5距离最远。转录分析显示acTLR5在蜥蜴的多个组织中表达。用TLR配体刺激acTLR5表明，在爬行动物和人类细胞中，其对细菌鞭毛蛋白具有独特的反应性。使用纯化的鞭毛蛋白对acTLR5和人类TLR5进行比较，发现其对铜绿假单胞菌鞭毛蛋白而非鼠伤寒沙门氏菌鞭毛蛋白的敏感性存在差异，这表明在哺乳动物和爬行动物的趋异进化过程中，物种特异性鞭毛蛋白识别得以发展。我们对爬行动物TLR5的发现填补了脊椎动物TLR保守性方面的进化空白，并为宿主 - 微生物相互作用的功能进化提供了新的见解。
