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Elena Conti

Publications and source records attributed to Elena Conti.

At least 37 records · Page 2Linked to original sources
PubMed2005

The archaeal exosome core is a hexameric ring structure with three catalytic subunits.

The exosome is a 3' --> 5' exoribonuclease complex involved in RNA processing. We report the crystal structure of the RNase PH core complex of the Sulfolobus solfataricus exosome determined at a resolution of 2.8 A. The structure reveals a hexameric ring-like arrangement of three Rrp41-Rrp42 heterodimers, where both subunits adopt the RNase PH fold common to phosphorolytic exoribonucleases. Structure-guided mutagenesis reveals that the activity of the complex resides within the active sites of the Rrp41 subunits, all three of which face the same side of the hexameric structure. The Rrp42 subunit is inactive but contributes to the structuring of the Rrp41 active site. The high sequence similarity of this archaeal exosome to eukaryotic exosomes and its high structural similarity to the bacterial mRNA-degrading PNPase support a common basis for RNA-degrading machineries in all three domains of life.

Amino Acid Sequence↗
PubMed2005

The structure of the nuclear export receptor Cse1 in its cytosolic state reveals a closed conformation incompatible with cargo binding.

Cse1 mediates nuclear export of importin alpha, the nuclear localization signal (NLS) import adaptor. We report the 3.1 A resolution structure of cargo-free Cse1, representing this HEAT repeat protein in its cytosolic state. Cse1 is compact, consisting of N- and C-terminal arches that interact to form a ring. Comparison with the structure of cargo-bound Cse1 shows a major conformational change leading to opening of the structure upon cargo binding. The largest structural changes occur within a hinge region centered at HEAT repeat 8. This repeat contains a conserved insertion that connects the RanGTP and importin alpha contact sites and that is essential for binding. In the cargo-free state, the RanGTP binding sites are occluded and the importin alpha sites are distorted. Mutations that destabilize the N- to C-terminal interaction uncouple importin alpha and Ran binding, suggesting that the closed conformation prevents association with importin alpha.

Active Transport, Cell Nucleus↗
PubMed2005

SMG7 is a 14-3-3-like adaptor in the nonsense-mediated mRNA decay pathway.

In metazoa, regulation of the phosphorylation state of UPF1 is crucial for nonsense-mediated mRNA decay (NMD), a process by which aberrant mRNAs containing nonsense mutations are degraded. UPF1 is targeted for dephosphorylation by three related proteins, SMG5, SMG6, and SMG7. We report here the crystal structure of the N-terminal domain of SMG7. The structure reveals that SMG7 contains a 14-3-3-like domain. Residues that bind phosphoserine-containing peptides in 14-3-3 are conserved at the equivalent positions in SMG7. Mutation of these residues impairs UPF1 binding to SMG7 in vitro and UPF1 recruitment to cytoplasmic mRNA decay foci in vivo, suggesting that SMG7 acts as an adaptor in targeting mRNAs associated with phosphorylated UPF1 for degradation. The 14-3-3 site of SMG7 is conserved in SMG5 and SMG6. These data also imply that the homologous human Est1 might have a 14-3-3 function at telomeres, and that phosphorylation events may be important for telomerase regulation.

14-3-3 Proteins↗
PubMed2005

Floral odor variation in two heterostylous species of Primula.

Floral traits such as odor, color, and morphology are important pollinator attractants. Variation in floral traits may influence floral constancy, the tendency of pollinating insects to visit flowers of only one type. We investigated for the first time variation in odor between floral morphs in heterostylous species. We analyzed inter- and intraspecific odor variation in the "pin" and "thrum" floral morphs of sympatric Primula elatior and P. farinosa (Primulaceae). Floral volatiles were sampled with headspace sorption. Quantitative analysis and chemical identification were performed by gas chromatography coupled to mass spectrometry. The species produced different floral bouquets. P. elatior emitted mostly limonene with small amounts of alpha-pinene, myrcene, and sabinene. P. farinosa produced benzaldehyde, 4-oxoisophorone (2,6,6-trimethyl-2-cyclohexene-1,4-dione), benzyl alcohol, and benzyl acetate. These interspecific differences may play a role in promoting floral constancy and maintaining species integrity. Conversely, no differences were detected between the scents of pin and thrum morphs within each species. Heterostyly relies on pollinators visiting both floral morphs. There may be stabilizing selection against divergences in traits that may cause pollinators to develop floral constancy to only one of the floral morphs.

Animals↗
PubMed2005

Nonsense-mediated mRNA decay: molecular insights and mechanistic variations across species.

Nonsense-mediated mRNA decay (NMD) is an mRNA surveillance pathway that ensures the rapid degradation of mRNAs containing premature translation termination codons (PTCs), thereby preventing the synthesis of truncated and potentially harmful proteins. In addition, this pathway regulates the expression of approximately 10% of the transcriptome and is essential in mice. Although NMD is conserved in eukaryotes, recent studies in several organisms have revealed that different mechanisms have evolved to discriminate natural from premature stop codons and to degrade the targeted mRNAs. With the elucidation of the first crystal structures of components of the NMD machinery, the way is paved towards a molecular understanding of the protein interaction network underlying this process.

Animals↗
PubMed2004

The superhelical TPR-repeat domain of O-linked GlcNAc transferase exhibits structural similarities to importin alpha.

Addition of N-acetylglucosamine (GlcNAc) is a ubiquitous form of intracellular glycosylation catalyzed by the conserved O-linked GlcNAc transferase (OGT). OGT contains an N-terminal domain of tetratricopeptide (TPR) repeats that mediates the recognition of a broad range of target proteins. Components of the nuclear pore complex are major OGT targets, as OGT depletion by RNA interference (RNAi) results in the loss of GlcNAc modification at the nuclear envelope. To gain insight into the mechanism of target recognition, we solved the crystal structure of the homodimeric TPR domain of human OGT, which contains 11.5 TPR repeats. The repeats form an elongated superhelix. The concave surface of the superhelix is lined by absolutely conserved asparagines, in a manner reminiscent of the peptide-binding site of importin alpha. Based on this structural similarity, we propose that OGT uses an analogous molecular mechanism to recognize its targets.

Acetylglucosamine↗
PubMed2004

Determinants for Aurora-A activation and Aurora-B discrimination by TPX2.

The mitotic kinases Aurora-A and Aurora-B have similar amino-acid sequences but are differently localised and regulated during cell division. The basis for their interactions with different and specific regulators is unclear. Surprisingly, our recent structural studies indicate that TPX2 regulates Aurora-A activity by binding at a site that is conserved almost completely on Aurora-B. Here we investigate molecular determinants of TPX2-Aurora-A recognition. Using structure-based mutagenesis, we show that a single amino-acid difference on the surface of the kinase catalytic domain is key to the precision with which TPX2 discriminates between Aurora-A and Aurora-B. The conservation at this amino-acid position suggests that this discriminatory mechanism is likely to be conserved in higher eukaryotes.

Animals↗
PubMed2004

Molecular insights into the interaction of PYM with the Mago-Y14 core of the exon junction complex.

The exon junction complex (EJC) is deposited on mRNAs as a consequence of splicing and influences postsplicing mRNA metabolism. The Mago-Y14 heterodimer is a core component of the EJC. Recently, the protein PYM has been identified as an interacting partner of Mago-Y14. Here we show that PYM is a cytoplasmic RNA-binding protein that is excluded from the nucleus by Crm1. PYM interacts directly with Mago-Y14 by means of its N-terminal domain. The crystal structure of the Drosophila ternary complex at 1.9 A resolution reveals that PYM binds Mago and Y14 simultaneously, capping their heterodimerization interface at conserved surface residues. Formation of this ternary complex is also observed with the human proteins. Mago residues involved in the interaction with PYM have been implicated in nonsense-mediated mRNA decay (NMD). Consistently, human PYM is active in NMD tethering assays. Together, these data suggest a role for PYM in NMD.

Amino Acid Sequence↗
PubMed2003

Conformational variability of nucleo-cytoplasmic transport factors.

The transport of macromolecules between the nucleus and cytoplasm of eukaryotic cells is largely mediated by a single family of transport factors, the karyopherin or importin beta-like family. Structural and biochemical evidence suggests conformational flexibility of these modular HEAT-repeat proteins is crucial for their regulation. Here we use small angle x-ray scattering to assess the extent of conformational variation within a set of nuclear import and export factors. The study reveals that importin beta, transportin, and the exportin Xpo-t share a similar S-like superhelical conformation in their unbound state. There are no obvious differences in the overall structures that might generally distinguish nuclear export from nuclear import mediators. Two other members of the family, the exportins Cse1 and Xpo1, possess a significantly more globular conformation, indicating that the extended S-like architecture is not a hallmark of all karyopherins. Binding of RanGTP/cargo to importin beta, transportin, and Xpo-t triggers distinct conformational responses, suggesting that even closely related karyopherins employ different mechanisms of conformational regulation and that cargo and nuclear pore-interacting surfaces of the different receptors may be unique.

Karyopherins↗
PubMed2003

Structural basis of Aurora-A activation by TPX2 at the mitotic spindle.

Aurora-A is an oncogenic kinase essential for mitotic spindle assembly. It is activated by phosphorylation and by the microtubule-associated protein TPX2, which also localizes the kinase to spindle microtubules. We have uncovered the molecular mechanism of Aurora-A activation by determining crystal structures of its phosphorylated form both with and without a 43 residue long domain of TPX2 that we identified as fully functional for kinase activation and protection from dephosphorylation. In the absence of TPX2, the Aurora-A activation segment is in an inactive conformation, with the crucial phosphothreonine exposed and accessible for deactivation. Binding of TPX2 triggers no global conformational changes in the kinase but pulls on the activation segment, swinging the phosphothreonine into a buried position and locking the active conformation. The recognition between Aurora-A and TPX2 resembles that between the cAPK catalytic core and its flanking regions, suggesting this molecular mechanism may be a recurring theme in kinase regulation.

Amino Acid Sequence↗
PubMed2003

The hitchhiker's guide to the nucleus.

The hormone-related protein PTHrP travels from the cytosol to the nucleus by binding to the transport factor importin . Remarkably, the site of recognition of PTHrP is the N-terminal half of importin , which also has Ran-binding and nucleoporin-binding capabilities and is, therefore, sufficient by itself to function in PTHrP nuclear import.

Active Transport, Cell Nucleus↗
PubMed2003

A novel mode of RBD-protein recognition in the Y14-Mago complex.

Y14 and Mago are conserved eukaryotic proteins that associate with spliced mRNAs in the nucleus and remain associated at exon junctions during and after nuclear export. In the cytoplasm, Y14 is involved in mRNA quality control via the nonsense-mediated mRNA decay (NMD) pathway and, together with Mago, is involved in localization of osk (oskar) mRNA. We have determined the crystal structure of the complex between Drosophila melanogaster Y14 and Mago at a resolution of 2.5 A. The structure reveals an atypical mode of protein-protein recognition mediated by an RNA-binding domain (RBD). Instead of binding RNA, the RBD of Y14 engages its RNP1 and RNP2 motifs to bind Mago. Using structure-guided mutagenesis, we show that Mago is also a component of the NMD pathway, and that its association with Y14 is essential for function. Heterodimerization creates a single structural platform that interacts with the NMD machinery via phylogenetically conserved residues.

Amino Acid Sequence↗
PubMed2003

Structural similarity in the absence of sequence homology of the messenger RNA export factors Mtr2 and p15.

The association between Mtr2 and Mex67 is essential for the nuclear export of bulk messenger RNA in yeast. In metazoans, the analogous function is carried out by the TAP-p15 heterodimer. Whereas Mex67 and TAP are highly conserved proteins, their binding partners, Mtr2 and p15, share no sequence similarity, but are nevertheless functionally homologous. Here, we report the 2.8-A resolution crystal structure of Mtr2 in complex with the NTF2-like domain of Mex67. Mtr2 is a novel member of the NTF2-like family and interacts with Mex67, forming a complex with a similar structural architecture to that of TAP-p15. Mtr2 fulfils an analogous function to that of human p15 in maintaining the structural integrity of the heterodimer. In addition, Mtr2 presents a long internal loop, which contains residues that affect the export of the large ribosomal subunit.

Amino Acid Sequence↗