title: Structural characterization and evolutionary analysis of fish-specific TLR27.
abstract: Toll-like receptors (TLRs) are critical components of the innate immune response of fish. In a phylogenetic analysis, TLR27 from three fish species, which belongs to TLR family 1, clustered with TLR14/18 and TLR25 on the evolutionary tree. The ectodomain of TLR27 is predicted to include 19 leucine-rich repeat (LRR) modules. Structural modeling showed that the TLR27 ectodomain can be divided into three distinctive sections. The lack of conserved asparagines on the concave surface of the central subdomain causes a structural transition in the middle of the ectodomain, forming a distinct hydrophobic pocket at the border between the central subdomain and the C-terminal subdomain. We infer that, like other functionally characterized TLRs in family 1, the hydrophobic pocket located between LRR11 and LRR12 participates in ligand recognition by TLR27. An evolutionary analysis showed that the dN/dS value at the TLR27 locus was very low. Approximately one quarter of the total number of TLR27 sites are under significant negatively selection pressure, whereas only two sites are under positive selection. Consequently, TLR27 is highly evolutionarily conserved and probably plays an extremely important role in the innate immune systems of fishes.
authors.affiliation: Institute of Developmental Biology, School of Life Science, Shandong University, Jinan 250100, PR China.
authors.forename: Jinlan
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Science, Shandong University, Jinan 250100, PR China. Electronic address: zhzhang@mail.sdu.edu.cn.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Institute of Developmental Biology, School of Life Science, Shandong University, Jinan 250100, PR China.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: Institute of Developmental Biology, School of Life Science, Shandong University, Jinan 250100, PR China.
authors.forename: Fang
authors.initials: F
authors.lastname: Li
authors.affiliation: Institute of Developmental Biology, School of Life Science, Shandong University, Jinan 250100, PR China.
authors.forename: Fen
authors.initials: F
authors.lastname: Chang
authors.affiliation: Institute of Developmental Biology, School of Life Science, Shandong University, Jinan 250100, PR China.
authors.forename: Hui
authors.initials: H
authors.lastname: Fu
authors.affiliation: Institute of Developmental Biology, School of Life Science, Shandong University, Jinan 250100, PR China.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Department of Internal Medicine, College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA. Electronic address: yin@etsu.edu.
authors.forename: Deling
authors.initials: D
authors.lastname: Yin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005399:Fishes / Q000235:genetics* / Q000378:metabolism; D008024:Ligands; D010802:Phylogeny; D012641:Selection, Genetic; D016415:Sequence Alignment; D013045:Species Specificity; D051193:Toll-Like Receptors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D029941:Fish Proteins; D008024:Ligands; D051193:Toll-Like Receptors
keywords: Innate immunity; Molecular evolution; PAMPs; Structural characteristics; Toll-like receptor 27