The Ubiquity of Iodotyrosine Deiodinase: Identification of its Signature Sequence and Functional Analysis in a Model Invertebrate

Iodotyrosine deiodinase (IYD) serves a critical role in iodide conservation through salvage of iodide from mono- and diiodotyrosine (I-Tyr and I2-Tyr), the by-products of thyroid hormone (TH) synthesis. Genomic data suggested the presence of this enzyme in a wide range of organisms including non-chordate invertebrates as well as prokaryotes. These organisms are not associated with TH signaling. A representative set of IYD homologs from these organisms with conserved key residues were expressed, purified and shown to catalyze deiodination of I2-Tyr with comparable catalytic efficiencies (kcat/Km). Our findings implied that the origins of IYD predate the evolution of TH signaling and suggested alternative physiological roles for IYD in non-chordate invertebrates. The IYD homolog from the model non-chordate invertebrate Drosophila melanogaster (dmIYD) displayed little discrimination between iodo-, bromo- and chlorotyrosine as substrates in vitro since all exhibited similar affinities and comparable efficiencies of dehalogenation. Additionally, active site mutants of dmIYD revealed a glutamate to be most critical for catalysis followed by a lysine while substitution of a tyrosine was least perturbing. These findings should further facilitate annotation of genomic data for potential halotyrosine dehalogenases. The in vivo function of the dehalogenase in non-chordate invertebrates is unknown. Prior expression profiling of mRNA in Drosophila indicated that testes expressed the highest level of the dehalogenase encoding gene (CG6279). This was confirmed through in situ hybridization experiments suggesting a biological role for CG6279 in spermatogenesis. However, deletion of the CG6279 gene (CG6279Del) as well as introduction of a loss of function amino acid substitution in the dehalogenase domain (CG6279E154Q) using CRISPR/Cas9 gene editing did not significantly affect the fertility of male Drosophila. This indicated that the dehalogenase gene is not critical for spermatogenesis. Previous studies demonstrated I-Tyr to be toxic to Drosophila larvae. To assess whether loss of function mutations in CG6279 increases larval sensitivity to I-Tyr toxicity, 1st instar larvae from both CG6279 mutant strains were raised on media supplemented with I-Tyr and survival to adulthood was evaluated. CG6279E154Q larvae displayed significantly lower survival rates in presence of I-Tyr compared to controls indicating increased sensitivity to I-Tyr toxicity. However, CG6279Del larvae were significantly less sensitive to I-Tyr toxicity leading to uncertainty whether the dehalogenase is metabolically active in vivo

Looking Back - The History of Biochemistry in India

The name Biochemistry was coined in 1903 by a German chemist named Carl Neuber. However, work in this very living, aspect of chemistry had started much earlier..

Looking Back - The History of Biochemistry in India

The name Biochemistry was coined in 1903 by a German chemist named Carl Neuber. However, work in this very living, aspect of chemistry had started much earlier..

Characterization of iodine-related molecular processes in the marine microalga Tisochrysis lutea (Haptophyta)

Iodine metabolism is essential for the antioxidant defense of marine algae and in the biogeochemical cycle of iodine. Moreover, some microalgae can synthetize thyroid hormone-like compounds that are essential to sustain food webs. However, knowledge regarding iodine-related molecular processes in microalgae is still scarce. In this study, a de novo transcriptome of Tisochrysis lutea cultured under high iodide concentrations (5 mM) was assembled using both long and short reads. A database termed IsochrysisDB was established to host all genomic information. Gene expression analyses during microalgal growth showed that most of the antioxidant- (aryl, ccp, perox, sod1, sod2, sod3, apx3, ahp1) and iodide-specific deiodinase (dio) genes increased their mRNA abundance progressively until the stationary phase to cope with oxidative stress. Moreover, the increase of dio mRNA abundance in aging cultures indicated that this enzyme was also involved in senescence. Cell treatments with iodide modified the expression of perox whereas treatments with iodate changed the transcript levels of gpx1 and ccp. To test the dependence of perox on iodide, microalgae cells were treated with hydrogen peroxide (H2O2) either in presence or absence of iodide observing that several genes related to reactive oxygen species (ROS) deactivation (perox, gpx1, apx2, apx3, ahp1, ahp2, sod1, sod3, and aryl) were transcriptionally activated although with some temporal differences. However, only the expression of perox was dependent on iodide levels indicating this enzyme, acquired by horizontal gene transfer (HGT), could act as a haloperoxidase. All these data indicate that T. lutea activates coordinately the expression of antioxidant genes to cope with oxidative stress. The identification of a phase-regulated deiodinase and a novel haloperoxidase provide new clues about the origin and evolution of thyroid signaling and the antioxidant role of iodine in the marine environment