Crystal structure of Trbp111: a structure-specific tRNA-binding protein

Trbp111 is a 111 amino acid Aquifex aeolicus structure-specific tRNA-bindin g protein that has homologous counterparts distributed throughout evolution . A dimer is the functional unit for binding a single tRNA. Here we report the 3D structures of the A.aeolicus protein and its Escherichia coli homolo g at resolutions of 2.50 and 1.87 Angstrom, respectively. The structure sho ws a symmetrical dimer of two core domains and a central dimerization domai n where the N- and C-terminal regions of Trbp111 form an extensive dimer in terface, The core of the monomer is a classical oligonucleotide/oligosaccha ride-binding (OB) fold with a five-stranded beta -barrel and a small cappin g helix. This structure is similar to that seen in the anticodon-binding do main of three class II tRNA synthetases and several other proteins. Mutatio nal analysis identified sites important for interactions with tRNA. These r esidues line the inner surfaces of two clefts formed between the beta -barr el of each monomer and the dimer interface. The results are consistent with a proposed model for asymmetrical docking of the convex side of tRNA to th e dimer.