Post-Transcriptional Control of Selenoprotein Biosynthesis

Selenoproteins are defined as proteins containing the 21st proteinogenic amino acid, selenocysteine (Sec). Sec is encoded by UGA (STOP) codons which are re-coded to Sec by the presence of a selenocysteine insertion sequence (SECIS) element in the 3'-untranslated region of selenoprotein mRNAs. The SECIS element is bound by several proteins, including SECIS-binding protein 2 (SBP2). Translation of selenoproteins critically depends on the integrity of the SECIS element – SBP2 interaction. Mutations in a SECIS element can abrogate expression of the respective selenoprotein. Mutations in SBP2 impinge on biosynthesis of a subset of selenoproteins and lead to a syndrome including hormonal, neurological, immunological symptoms as well as myopathy. Several other RNA-binding proteins are involved in selenoprotein translation and mediate the hierarchical response of selenoproteins to selenium deficiency. Global inhibition of selenoprotein translation is lethal in the mouse and hypomorphic mutations in selenocysteine synthase in humans leads to Progressive Cerebello Cerebral Atrophy, a neurodevelopmental and neurodegenerative disease in pediatric patients.