Type 2 iodothyronine deiodinase (DIO2)

Type 2 iodothyronine deiodinase (DIO2) is a critical selenoenzyme responsible for the intracellular activation of the prohormone thyroxine (T4) into the biologically active triiodothyronine (T3) [1, 4]. Unlike Type 1 deiodinase, which contributes significantly to circulating T3, DIO2 primarily regulates local T3 availability in tissues such as the brain, pituitary gland, skeletal muscle, and brown adipose tissue [3, 10]. This localized control is essential for maintaining thyroid hormone homeostasis, regulating adaptive thermogenesis, and ensuring proper neurodevelopment and muscle regeneration [1, 5]. DIO2 activity is uniquely regulated by a substrate-induced ubiquitination process, where T4 binding triggers its inactivation and subsequent proteasomal degradation, providing a rapid "on/off" switch for thyroid signaling [4, 6]. Clinically, DIO2 is a significant therapeutic target and biomarker. The common Thr92Ala polymorphism in the DIO2 gene is associated with reduced enzymatic efficiency and has been linked to residual hypothyroid symptoms in patients on levothyroxine monotherapy, as well as increased risks for type 2 diabetes, obesity, and neurodegenerative diseases [7, 11, 16]. Pharmacological modulation of DIO2, such as through bile acids or specific flavonols like kaempferol, offers potential avenues for treating metabolic disorders by enhancing energy expenditure [5, 6]. Conversely, its inhibition by drugs like amiodarone or iopanoic acid can disrupt the hypothalamic-pituitary-thyroid feedback loop, leading to altered TSH levels and localized thyroid hormone deficiency [5, 15].

Other names

D2Iodothyronine deiodinase type IISelenoprotein DIO2ITDI2TXDI25'-deiodinase type II

Type 2 iodothyronine deiodinase (DIO2) catalyzes the outer-ring deiodination of the prohormone thyroxine (T4) to the active hormone triiodothyronine (T3) [1, 4]. It is a homodimeric thioredoxin-fold containing selenoprotein that utilizes a selenocysteine residue in its catalytic center [4, 6]. The enzyme's activity is tightly regulated by a substrate-induced ubiquitination-deubiquitination switch; T4 binding triggers ubiquitination by E3 ligases (WSB-1, TEB4), leading to inactivation and proteasomal degradation, while deubiquitinases (USP20, USP33) can rescue and reactivate the enzyme [5, 6].