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Identification of a transcript encoding a soluble form of toll-like receptor 5 (TLR5) in Atlantic salmon during Aeromonas salmonicida infection

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Abstract

Toll-like receptors (TLRs) are involved in the innate immune response against microbial pathogens in vertebrates and insects. The extracellular region of a TLR recognizes pathogen-associated molecules, while the intracellular region initiates the signaling pathway leading to immune response. Membrane-bound TLRs have been found in most vertebrates, but few soluble forms have been reported. A novel transcript corresponding to a portion of a soluble TLR was identified in liver of infected Atlantic salmon. The complete coding sequence of this TLR was obtained and BLASTN analysis showed the highest sequence identity to a recently described full-length cDNA sequence of a soluble TLR5 from rainbow trout (GenBank Accession No.: AB062504). The deduced protein is 40% identical to the mammalian counterpart of the leucine-rich repeat (LRR)/LRR-like motifs of TLR5. Based on the structure of human TLRs, it contains 21 LRRs with conserved LxxLxLxxNx*xx*xxxxFxxL pattern. Since TLR5 is essential for the recognition of bacterial flagellins, we hypothesize that flagellin and perhaps some other pathogen-derived factors from Aeromonas salmonicida bind to this soluble TLR through an unknown binding domain within the LRR.

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Acknowledgements

We are grateful to Andrew Dacanay, Jeff Gallant, Sandra Sperker and Bob Richards (all NRC IMB) for technical support. NRC IMB and the NRC Genomics and Health Initiative supported this study. The corresponding author acknowledges critical review of manuscript and encouragement from Dr. Brian Kay, Argonne National Laboratory, Argonne, IL 60439-4833, United States. This is NRC publication number 42490.

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The sequence reported in this paper has been deposited in the GenBank database (Accession No. AY628755).

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