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Comp Biochem Physiol B Biochem Mol Biol. 2013 Mar;164(3):143-50. doi: 10.1016/j.cbpb.2012.12.003. Epub 2012 Dec 20.

Identification and bioactivity analysis of transthyretin-like protein in amphioxus: a case demonstrating divergent evolution from an enzyme to a hormone distributor.

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1
Laboratory for Evolution & Development, Institute of Evolution & Marine Biodiversity and Department of Marine Biology, Ocean University of China, Qingdao 266003, China.

Abstract

Transthyretin-like proteins are a family of proteins that share remarkable structural similarities to transthyretin, that have been identified in a variety of taxa such as bacteria, fungi, plants, invertebrates and vertebrates. Despite the enormous progress in the study of transthyretin-like protein, little is known about it in amphioxus, a model organism for insights into the origin and evolution of vertebrates. Here we identified a transthyretin-like protein gene in Branchiostoma japonicum, named Bjtlp, which possessed a TLP-HIUase (an enzyme hydrolyzing 5-hydroxyisourate) domain and a consensus C-terminal tetrapeptide Tyr-Arg-Gly-Ser that are both characteristics of all known transthyretin-like proteins. Phylogenetic and intron-exon structure analyses support that TTR likely arose from a vertebrate specific duplication after vertebrates diverged from invertebrate chordates. Quantitative real-time PCR analysis revealed that Bjtlp was expressed in a tissue-specific fashion, with the transcript levels being most abundant in the hepatic caecum and hind gut. Enzymatic activity assays demonstrated that recombinant BjTLP had the capacity to hydrolyze 5-hydroxyisourate. Site-directed mutagenesis showed that both Y156 and R93 residues were critical for 5-hydroxyisourate hydrolase activity of recombinant BjTLP. Moreover, the single mutation, Y156T, at the active site of BjTLP caused approximately 97% loss of its enzymatic activity, and meanwhile gained the thyroxine binding activity. All these data together suggest that the single mutation Y156T is critical for converting BjTLP to a new transport protein capable of distributing thyroxine.

PMID:
23262064
DOI:
10.1016/j.cbpb.2012.12.003
[Indexed for MEDLINE]
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