title: Crystal structures of the human elongation factor eEFSec suggest a non-canonical mechanism for selenocysteine incorporation.
abstract: Selenocysteine is the only proteinogenic amino acid encoded by a recoded in-frame UGA codon that does not operate as the canonical opal stop codon. A specialized translation elongation factor, eEFSec in eukaryotes and SelB in prokaryotes, promotes selenocysteine incorporation into selenoproteins by a still poorly understood mechanism. Our structural and biochemical results reveal that four domains of human eEFSec fold into a chalice-like structure that has similar binding affinities for GDP, GTP and other guanine nucleotides. Surprisingly, unlike in eEF1A and EF-Tu, the guanine nucleotide exchange does not cause a major conformational change in domain 1 of eEFSec, but instead induces a swing of domain 4. We propose that eEFSec employs a non-canonical mechanism involving the distinct C-terminal domain 4 for the release of the selenocysteinyl-tRNA during decoding on the ribosome.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Dobosz-Bartoszek
authors.affiliation: Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Pinkerton
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: Zbyszek
authors.initials: Z
authors.lastname: Otwinowski
authors.affiliation: Biophysics Collaborative Access Team/Illinois Institute of Technology, Sector 18ID, Advanced Photon Source, Chicago, Illinois 60439, USA.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Chakravarthy
authors.affiliation: Departments of Molecular Biophysics and Biochemistry, and Chemistry, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Dieter
authors.initials: D
authors.lastname: Söll
authors.affiliation: Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Copeland
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
authors.forename: Miljan
authors.initials: M
authors.lastname: Simonović
mesh_terms: D018388:Codon, Terminator; D018360:Crystallography, X-Ray; D006153:Guanosine Diphosphate / Q000737:chemistry; D006160:Guanosine Triphosphate / Q000737:chemistry; D006801:Humans; D010445:Peptide Elongation Factors / Q000737:chemistry*; D010802:Phylogeny; D014176:Protein Biosynthesis; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry; D012270:Ribosomes / Q000378:metabolism; D017279:Selenocysteine / Q000737:chemistry*; D051140:Selenoproteins / Q000235:genetics
chemical_list: D018388:Codon, Terminator; C535118:EEFSEC protein, human; D010445:Peptide Elongation Factors; D012346:RNA, Transfer, Amino Acyl; D051140:Selenoproteins; C112705:selenocysteinyl-tRNA; D017279:Selenocysteine; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate