Crystal structure of an mRNA-binding fragment of Moorella thermoacetica elongation factor SelB

• Published in: The EMBO journal Vol. 21; no. 15; pp. 4145 - 4153
• Main Authors: Selmer, M., Su, X.-D.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2002; Blackwell Publishing Ltd; Oxford University Press
• Subjects: Amino Acid Sequence; Amino Acid Substitution; Amino acids; Bacterial Proteins - chemistry; Binding Sites; Biochemistry and Molecular Biology; Biokemi och molekylärbiologi; Biologi; Biological Sciences; Clostridium - chemistry; crystallography; Crystallography, X-Ray; elongation factor; Models, Molecular; Molecular Sequence Data; Mutation, Missense; Natural Sciences; Naturvetenskap; Peptide Elongation Factors - chemistry; Protein Conformation; Protein Structure, Tertiary; Ribosomes - metabolism; RNA binding; RNA, Bacterial - metabolism; RNA, Messenger - metabolism; RNA, Transfer - metabolism; SelB; Selenium; selenocysteine; Sequence Alignment; Sequence Homology, Amino Acid; Sulfates - chemistry; Yttrium
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/cdf408

SelB is an elongation factor needed for the co‐translational incorporation of selenocysteine. Selenocysteine is coded by a UGA stop codon in combination with a specific downstream mRNA hairpin. In bacteria, the C‐terminal part of SelB recognizes this hairpin, while the N‐terminal part binds GTP and tRNA in analogy with elongation factor Tu (EF‐Tu). We present the crystal structure of a C‐terminal fragment of SelB (SelB‐C) from Moorella thermoacetica at 2.12 Å resolution, solved by a combination of selenium and yttrium multiwavelength anomalous dispersion. This 264 amino acid fragment contains the entire C‐terminal extension beginning after the EF‐Tu‐homologous domains. SelB‐C consists of four similar winged‐helix domains arranged into the shape of an L. This is the first example of winged‐helix domains involved in RNA binding. The location of conserved basic amino acids, together with data from the literature, define the position of the mRNA‐binding site. Steric requirements indicate that a conformational change may occur upon ribosome interaction. Struc tural observations and data in the literature suggest that this change happens upon mRNA binding.