Selenocysteine tRNA-specific elongation factor SelB is a structural chimaera of elongation and initiation factors
Copyright policy )Selenocysteine tRNA-specific elongation factor SelB is a structural chimaera of elongation and initiation factors
In all three kingdoms of life, SelB is a specialized translation elongation factor responsible for the cotranslational incorporation of selenocysteine into proteins by recoding of a UGA stop codon in the presence of a downstream mRNA hairpin loop. Here, we present the X-ray structures of SelB from the archaeon Methanococcus maripaludis in the apo-, GDP- and GppNHp-bound form and use mutational analysis to investigate the role of individual amino acids in its aminoacyl-binding pocket. All three SelB structures reveal an EF-Tu:GTP-like domain arrangement. Upon binding of the GTP analogue GppNHp, a conformational change of the Switch 2 region in the GTPase domain leads to the exposure of SelB residues involved in clamping the 5' phosphate of the tRNA. A conserved extended loop in domain III of SelB may be responsible for specific interactions with tRNA(Sec) and act as a ruler for measuring the extra long acceptor arm. Domain IV of SelB adopts a beta barrel fold and is flexibly tethered to domain III. The overall domain arrangement of SelB resembles a 'chalice' observed so far only for initiation factor IF2/eIF5B. In our model of SelB bound to the ribosome, domain IV points towards the 3' mRNA entrance cleft ready to interact with the downstream secondary structure element.
- Ludwig-Maximilians-Universität München Germany
- ETH Zurich Switzerland
- Institute of Molecular Biology and Biophysics Switzerland
Models, Molecular, Binding Sites, Protein Conformation, Archaeal Proteins, Methanococcus, DNA Mutational Analysis, Molecular Sequence Data, Prokaryotic Initiation Factors, Crystallography, X-Ray, Peptide Elongation Factors, Guanosine Diphosphate, RNA, Transfer, Nucleic Acid Conformation, Amino Acid Sequence, Guanosine Triphosphate, Eukaryotic Initiation Factors, Sequence Alignment, Protein Binding
Models, Molecular, Binding Sites, Protein Conformation, Archaeal Proteins, Methanococcus, DNA Mutational Analysis, Molecular Sequence Data, Prokaryotic Initiation Factors, Crystallography, X-Ray, Peptide Elongation Factors, Guanosine Diphosphate, RNA, Transfer, Nucleic Acid Conformation, Amino Acid Sequence, Guanosine Triphosphate, Eukaryotic Initiation Factors, Sequence Alignment, Protein Binding
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