title: Enhanced antimicrobial peptide-induced activity in the mollusc Toll-2 family through evolution via tandem Toll/interleukin-1 receptor.
abstract: Toll receptors play an important role in the innate immunity of invertebrates. All reported Tolls have only one Toll/interleukin-1 receptor (TIR) domain at the C-terminal. In this study, numerous Tolls with tandem TIRs at the C-terminal were found in molluscs. Such Tolls presented an extra TIR (TIR-1) compared with Toll-I. Thus, Toll-I might be the ancestor of tandem TIRs containing Toll. To test this hypothesis, 83 Toll-I and Toll-2 (most have two TIRs, but others seem to be the evolutionary intermediates) genes from 29 shellfish species were identified. These Tolls were divided into nine groups based on phylogenetic analyses. A strong correlation between phylogeny and motif composition was found. All Toll proteins contained the TIR-2 domain, whereas the TIR-1 domain only existed in some Toll-2 protein, suggesting that TIR-1 domain insertion may play an important role in Toll protein evolution. Further analyses of functional divergence and adaptive evolution showed that some of the critical sites responsible for functional divergence may have been under positive selection. An additional intragenic recombination played an important role in the evolution of the Toll-I and Toll-2 genes. To investigate the functional difference of Toll-I and Toll-2, over expression of Hcu_Toll-I or Hcu_Toll-2-2 in Drosophila S2 cells was performed. Results showed that Hcu_Toll-2-2 had stronger antimicrobial peptide (AMP) activity than Hcu_Toll-I. Therefore, enhanced AMP-induced activity resulted from tandem TIRs in Toll-2s of molluscs during evolution history.
authors.affiliation: Institute of Life Sciences , Jiangsu University , Zhenjiang, Jiangsu , People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Cao
authors.affiliation: MOE Key Laboratory of Aquatic Product Safety/State Key Laboratory of Biocontrol, School of Marine Sciences , Sun Yat-sen University , Guangzhou , People's Republic of China.
authors.forename: Yihong
authors.initials: Y
authors.lastname: Chen
authors.affiliation: State Key Laboratory Breeding Base of Marine Genetic Resource , Third Institute of Oceanography , SOA, Xiamen 361005 , People's Republic of China.
authors.forename: Min
authors.initials: M
authors.lastname: Jin
authors.affiliation: Jiangsu Key Laboratory for Biodiversity and Biotechnology and Jiangsu Key Laboratory for Aquatic Crustacean Diseases, College of Life Sciences , Nanjing Normal University , Nanjing 210046 , People's Republic of China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Ren
keywords: Toll; evolution; mollusc; over expression; tandem Toll/interleukin-1 receptor