Selenium is an essential micronutrient for human health. The major biological form of selenium, the amino acid selenocysteine (Sec), is found in 25 human selenoproteins and selenoenzymes, many of which play pivotal roles in basic biological processes. The mechanism of selenium and Sec incorporation into the protein is the central and yet unresolved problem of selenium biology. The goal of this proposal is to unravel key steps of this process at the molecular and structural level. Unlike the 20 standard amino acids, Sec is delivered to the ribosome by a specialized elongation factor, eEFSec in eukaryotes and SelB in prokaryotes. Interestingly, Sec is encoded by an in-frame UGA codon, otherwise a translational stop codon. Accurate decoding and differentiation of Sec and stop UGA codons in humans requires auxiliary protein (SBP2) and RNA factors (SECIS), which are absent in the canonical gene translation machinery. Selenium deficiency, mutations in selenoprotein genes, and low levels of selenoproteins lead to diseases affecting nervous, endocrine, muscular, immune, and reproductive systems. Failure to incorporate Sec diminishes selenoenzyme activity and compromises selenoprotein structure, allowing for disease development. The deletion of the eEFSec gene obliterates selenoprotein synthesis, and mutations in human SBP2 and SECIS cause pathologies. Although unrelated to the general translation elongation factors, the Sec-UGA decoding and Sec incorporation are still being described using the inadequate canonical model of protein synthesis. To address this deficiency, several critical aspects of the process will be addressed in this proposal. First, the mechanism by which eEFSec selects Sec-tRNASec among other aminoacyl-tRNAs will be determined using X-ray crystallography and in vitro binding and activity assays. Also, the proposed stringent selectivity of eEFSec towards Sec will be assessed by an in vitro translation system and by analyses of selenoproteins. Secondly, the structure of SBP2, its role in decoding, and the impact of pathogenic mutations on its structure and function will be determined. Given our preliminary findings on human eEFSec, the proposed work will shift the paradigm about processes regulating translation of selenoprotein genes and will significantly advance our understanding of the aspects of co-translational incorporation of selenium and Sec that are conserved across kingdoms.

Public Health Relevance

Selenium, an essential micronutrient, is a constitutive component of 25 human proteins and enzymes, many of which are critical for health and survival. Mutations in selenoproteins and protein and RNA factors regulating synthesis of selenoproteins elicit systemic diseases in humans. The proposed study will explain how selenium is incorporated into selenoproteins at both the structural and molecular level. Our findings will provide novel information about the fundamental process governing faithful translation of human genes and provide mechanistic insights into a number of pathologies.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
Project #
Application #
Study Section
Integrative Nutrition and Metabolic Processes Study Section (INMP)
Program Officer
Ansong, Charles Kwaku
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Illinois at Chicago
Schools of Medicine
United States
Zip Code
Simonovi?, Miljan; Puppala, Anupama K (2018) On elongation factor eEFSec, its role and mechanism during selenium incorporation into nascent selenoproteins. Biochim Biophys Acta Gen Subj :
Ognjenovi?, Jana; Simonovi?, Miljan (2018) Human aminoacyl-tRNA synthetases in diseases of the nervous system. RNA Biol 15:623-634
Holman, Kaitlyn M; Puppala, Anupama K; Lee, Jonathan W et al. (2017) Insights into substrate promiscuity of human seryl-tRNA synthetase. RNA 23:1685-1699
Dobosz-Bartoszek, Malgorzata; Pinkerton, Mark H; Otwinowski, Zbyszek et al. (2016) Crystal structures of the human elongation factor eEFSec suggest a non-canonical mechanism for selenocysteine incorporation. Nat Commun 7:12941
Ognjenovi?, Jana; Wu, Jiang; Matthies, Doreen et al. (2016) The crystal structure of human GlnRS provides basis for the development of neurological disorders. Nucleic Acids Res 44:3420-31
Holman, Kaitlyn M; Wu, Jiang; Ling, Jiqiang et al. (2016) The crystal structure of yeast mitochondrial ThrRS in complex with the canonical threonine tRNA. Nucleic Acids Res 44:1428-39
Gladyshev, Vadim N; Arnér, Elias S; Berry, Marla J et al. (2016) Selenoprotein Gene Nomenclature. J Biol Chem 291:24036-24040
Puppala, Anupama K; French, Rachel L; Matthies, Doreen et al. (2016) Structural basis for early-onset neurological disorders caused by mutations in human selenocysteine synthase. Sci Rep 6:32563
Anttonen, Anna-Kaisa; Hilander, Taru; Linnankivi, Tarja et al. (2015) Selenoprotein biosynthesis defect causes progressive encephalopathy with elevated lactate. Neurology 85:306-15
French, Rachel L; Gupta, Nirupama; Copeland, Paul R et al. (2014) Structural asymmetry of the terminal catalytic complex in selenocysteine synthesis. J Biol Chem 289:28783-94

Showing the most recent 10 out of 14 publications