Structures of the tRNA export factor in the nuclear and cytosolic states

• Published in: Nature (London) 2009-09, Vol.461 (7260), p.60-65
• Main Authors: Cook, Atlanta G., Fukuhara, Noemi, Jinek, Martin, Conti, Elena
• Format: Article
• Language: English
• Subjects: Binding Sites; Biological and medical sciences; Biological transport; Carrier proteins; Cell Nucleus - metabolism; Crystalline structure; Crystallography, X-Ray; Crystals; Cytosol - metabolism; Data collection; E coli; Enzymes; Exports; Fundamental and applied biological sciences. Psychology; GTPase-Activating Proteins - chemistry; GTPase-Activating Proteins - metabolism; Humanities and Social Sciences; Models, Molecular; Molecular biophysics; multidisciplinary; Nuclear Pore Complex Proteins - chemistry; Nuclear Pore Complex Proteins - metabolism; Physiological aspects; Properties; Protein Binding; Protein Conformation; Quality control; ran GTP-Binding Protein - chemistry; ran GTP-Binding Protein - metabolism; Ribonucleic acid; RNA; RNA Transport; RNA, Fungal - chemistry; RNA, Fungal - genetics; RNA, Fungal - metabolism; RNA, Transfer - chemistry; RNA, Transfer - genetics; RNA, Transfer - metabolism; RNA, Transfer, Phe - chemistry; RNA, Transfer, Phe - genetics; RNA, Transfer, Phe - metabolism; Saccharomyces cerevisiae Proteins - chemistry; Saccharomyces cerevisiae Proteins - metabolism; Schizosaccharomyces pombe Proteins - chemistry; Schizosaccharomyces pombe Proteins - metabolism; Science; Structure; Structure in molecular biology; Substrate Specificity; Transfer RNA
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature08394

Transfer RNAs are among the most ubiquitous molecules in cells, central to decoding information from messenger RNAs on translating ribosomes. In eukaryotic cells, tRNAs are actively transported from their site of synthesis in the nucleus to their site of function in the cytosol. This is mediated by a dedicated nucleo-cytoplasmic transport factor of the karyopherin-β family (Xpot, also known as Los1 in Saccharomyces cerevisiae ). Here we report the 3.2 Å resolution structure of Schizosaccharomyces pombe Xpot in complex with tRNA and RanGTP, and the 3.1 Å structure of unbound Xpot, revealing both nuclear and cytosolic snapshots of this transport factor. Xpot undergoes a large conformational change on binding cargo, wrapping around the tRNA and, in particular, binding to the tRNA 5′ and 3′ ends. The binding mode explains how Xpot can recognize all mature tRNAs in the cell and yet distinguish them from those that have not been properly processed, thus coupling tRNA export to quality control. Keeping tRNA in its place After their transcription and processing, transfer RNAs are exported from the nucleus to the cytoplasm, where translation occurs. tRNAs are carried through pores in the nuclear membrane by a transport factor, Xpot. Now the structure of Xpot has been determined, alone and bound to both tRNA and to another factor required for transport, RanGTP. Binding of the tRNA induces large conformational changes so that Xpot encloses the tRNA and interacts with both its 5′ and 3′ ends. This explains an important mechanism of quality control in protein synthesis, by which unprocessed tRNAs, with immature ends, are prevented from being carried out of the nucleus. After transcription and processing, transfer RNAs must be exported from the nucleus to the cytoplasm, where translation occurs. This process is mediated by a dedicated nucleo-cytoplasmic transport factor called Xpot. Here, the structure of Schizosaccharomyces pombe Xpot is reported, unbound and in complex with both tRNA and another factor required for transport, RanGTP.