Structural and functional evolution of transthyretin and transthyretin‐like proteins

Abstract

Transthyretin (TTR) is a tetrameric protein involved in the distribution of thyroid hormones in vertebrates. The amino acid sequence of TTR is highly conserved across vertebrates. Hypothetical TTR-like proteins (TLPs) were inferred from the identification of genes in nonvertebrate species. Here, we identified five motifs defining TLPs and three motifs defining both TTRs and TLPs. These motifs were mapped onto structurally conserved and functionally important regions of TTRs. These motifs were used to build hidden Markov models for accurate identification of TLPs in other organisms. TLPs were divided into three main groups based on their N-terminal regions. Most TLPs are cytosolic, but in plants and slime mold, we predict they are peroxisomal. We verified that the TLPs from enterobacteria were periplasmic. We demonstrated that TLP genes are expressed in a bacterium (E. coli), an invertebrate animal (C. elegans), and a plant (A. thaliana). These TLPs have similar subunit molecular weights to TTRs, are tetramers, and are predicted to have similar three-dimensional (3D) structures to TTRs, but do not bind thyroid hormones or similar ligands. We suggest that like TTRs, the N-terminal and C-terminal regions of TLPs are integral in defining the function of TLPs in nonvertebrate species and that the TLP gene duplicated in primitive vertebrates to produce the TTR gene. TLP/TTR has retained its overall structure, but changed function and localization during evolution in bacteria, invertebrates, plants, and vertebrates.

Proteome Analysis ofArabidopsisLeaf Peroxisomes Reveals Novel Targeting Peptides, Metabolic Pathways, and Defense Mechanisms

“…Another protein spot (ATF1; At1g21770; SSI>) was identified as a closely related homolog of a recently crystallized minimal acetyl transferase (ATF2; At1g77540; SSI>; Tyler et al, 2006). The single Arabidopsis transthyretin-like protein (TLP; At5g58220) is homologous to mammalian transthyretin, a transport protein for vertebrate hormones (Eneqvist et al, 2003;Hennebry et al, 2006aHennebry et al, , 2006b. Interestingly, the full-length protein contains a predicted PTS2 (RLx 5 HL) outside of the N-terminal domain in a linker region that connects two enzymatic domains, whereas two alternative splice variants from Arabidopsis lack the putative targeting signal ( Figure 3A; see Supplemental Figure 3P online; Hennebry et al, 2006a;Ramazzina et al, 2006).…”

“…The single Arabidopsis transthyretin-like protein (TLP; At5g58220) is homologous to mammalian transthyretin, a transport protein for vertebrate hormones (Eneqvist et al, 2003;Hennebry et al, 2006aHennebry et al, , 2006b. Interestingly, the full-length protein contains a predicted PTS2 (RLx 5 HL) outside of the N-terminal domain in a linker region that connects two enzymatic domains, whereas two alternative splice variants from Arabidopsis lack the putative targeting signal ( Figure 3A; see Supplemental Figure 3P online; Hennebry et al, 2006a;Ramazzina et al, 2006). By MS sequencing of three tryptic peptides covering major parts of the linker region, including the putative PTS2, the TLP homolog identified in Arabidopsis peroxisomes was demonstrated to represent the full-length protein, strengthening the idea that the internal PTS2 peptide targets full-length TLP to peroxisomes (Figure 3).…”

Bioconcentration and metabolism of decabromodiphenyl ether (BDE-209) result in thyroid endocrine disruption in zebrafish larvae

“…The nitrocellulose membrane was blocked for 1 h with 5% non-fat dried milk in tris-buffered saline (TBS) and incubated with primary antibody against TG (Sigma, St. Louis, MO, USA)/TTR (Abcam, USA) at 37 • C for 2 h. The blots were washed six times for 30 min with tris-buffered saline Tween-20 (TBST) and then incubated with AP-conjugated secondary antibody at 37 • C for 1 h. After that the blots were washed six times again, they were developed using a BCIP/NBT Kit (AMRESCO, USA). TTR is considered as an evolutionarily conserved serum protein (Hennebry et al, 2006;Buxbaum and Reixach, 2009 (Morgado et al, 2007). Using a rabbit antihuman TG serum that cross-reacted with lampreys (Lampetra appendix) TG, Western blotting detected a single protein of ∼226 kDa (Manzon and Youson, 2002).…”

Hormone affinity and fibril formation of piscine transthyretin: The role of the N-terminal

“…Page 4 of 44 A c c e p t e d M a n u s c r i p t 4 proteins (TLPs) has been identified in bacteria, plants and animals including nonvertebrates and vertebrates (Eneqvist et al, 2003, Hennebry et al, 2006a. It has been suggested that the TTR gene, only present in vertebrates, probably arose as a results of a duplication of the ancestral TLP gene (Hennebry et al, 2006a, Prapunpoj et al, 2000, Richardson, 2002.…”

“…It has been suggested that the TTR gene, only present in vertebrates, probably arose as a results of a duplication of the ancestral TLP gene (Hennebry et al, 2006a, Prapunpoj et al, 2000, Richardson, 2002. Existent studies indicate an overall structural conservation between TLP and TTR (Hennebry et al, 2006b, Lundberg et al, 2006 however no evidence of TH binding ability could be found for TLP (Eneqvist et al, 2003).…”