Domain combination of the vertebrate-like TLR gene family: implications for their origin and evolution.
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.
Laboratory of Developmental Immunology, School of Life Science, Shandong University, Jinan 250100, People's Republic of China. edison_woo@yahoo.cn
Baojun
B
Wu
Tianxiao
T
Huan
Jing
J
Gong
Pin
P
Zhou
Zengliang
Z
Bai
D000818:Animals; D003063:Cnidaria / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000276:immunology; D019143:Evolution, Molecular; D007930:Leucine / Q000737:chemistry; D005810:Multigene Family; D010802:Phylogeny; D011161:Porifera / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D017434:Protein Structure, Tertiary; D017472:Receptors, Interleukin-1 / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D013045:Species Specificity; D051193:Toll-Like Receptors / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000276:immunology
D017472:Receptors, Interleukin-1; D051193:Toll-Like Receptors; D007930:Leucine