A viral deubiquitylating enzyme targets viral RNA-dependent RNA polymerase and affects viral infectivity.

International audienceSelective protein degradation via the ubiquitin-proteasome system (UPS) plays an essential role in many major cellular processes, including host-pathogen interactions. We previously reported that the tightly regulated viral RNA-dependent RNA polymerase (RdRp) of the positive-strand RNA virus Turnip yellow mosaic virus (TYMV) is degraded by the UPS in infected cells, a process that affects viral infectivity. Here, we show that the TYMV 98K replication protein can counteract this degradation process thanks to its proteinase domain. In-vitro assays revealed that the recombinant proteinase domain is a functional ovarian tumour (OTU)-like deubiquitylating enzyme (DUB), as is the 98K produced during viral infection. We also demonstrate that 98K mediates in-vivo deubiquitylation of TYMV RdRp protein-its binding partner within replication complexes-leading to its stabilization. Finally, we show that this DUB activity contributes to viral infectivity in plant cells. The identification of viral RdRp as a specific substrate of the viral DUB enzyme thus reveals the intricate interplay between ubiquitylation, deubiquitylation and the interaction between viral proteins in controlling levels of RdRp and viral infectivity

In praise of impurity: 30S ribosomal S15 protein-assisted crystallization of turnip yellow mosaic virus proteinase

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699Turnip yellow mosaic virus is an excellent model for eukaryotic positive-stranded RNA virus replication. Correct processing of the replication polyprotein is dependent on the virally encoded cysteine proteinase (PRO) domain. Crystalline needles obtained from highly pure preparations of the recombinant 17.6 kDa PRO did not diffract. In contrast, small hexagonal prisms that were obtained together with the needles under the same conditions but from a poorly purified preparation diffracted to 2 A resolution and allowed structure determination by MIRAS. It turned out that the hexagonal crystals contained stoichiometric amounts of PRO and Escherichia coli 30S ribosomal S15, a 10.1 kDa protein commonly co-purified by immobilized metal-affinity chromatography. The solvent content is nearly 70%, with S15 bridging parallel infinite helices of PRO across large solvent channels. With hindsight, this spurious interaction not only yielded diffraction-quality crystals but would also have allowed structure determination by molecular replacement using S15 as a search model and subsequent automatic rebuilding of the asymmetric unit

Insights into the activation of Kinesin1 from the molecular characterisation of JIP3/4 binding to Kif5b

International audienceAbstract Whereas our understanding of kinesin auto-inhibition mechanisms is improving faster, important insights into kinesin activation mechanisms such as those controlled by cargo-motor adaptors are still missing. JIP3 and JIP4 are versatile motor-cargo adaptors for kinesin1 and dynein-dynactin motors enabling bi-directional transport on microtubules. JIP3 activates kinesin1 heavy chains, independently of kinesin1 light chains. In this report, we characterize the molecular details of the binding of the kinesin1 heavy chain, Kif5b to the motor-cargo adaptors, JIP3 and JIP4, using biophysical approaches. The definition of the exact binding site of Kif5b, as well as the specificity of interaction between JIP3 and JIP4 provide new insights into kinesin1 activation

Structural snapshots of the kinesin-2 OSM-3 along its nucleotide cycle: implications for the ATP hydrolysis mechanism

Motile kinesins are motor proteins that translocate along microtubules as they hydrolyze ATP. They share a conserved motor domain which harbors both ATPase and microtubule-binding activities. An ATP hydrolysis mechanism involving two water molecules has been proposed based on the structure of the kinesin-5 Eg5 bound to an ATP analog. Whether this mechanism is general in the kinesin superfamily remains uncertain. Here, we present structural snapshots of the motor domain of OSM-3 along its nucleotide cycle. OSM-3 belongs to the homodimeric kinesin-2 subfamily and is the Caenorhabditis elegans homologue of human KIF17. OSM-3 bound to ADP or devoid of a nucleotide shows features of ADP-kinesins with a docked neck-linker. When bound to an ATP analog, OSM-3 adopts a conformation similar to those of several ATP-like kinesins, either isolated or bound to tubulin. Moreover, the OSM-3 nucleotide binding site is virtually identical to that of ATP-like Eg5, demonstrating a shared ATPase mechanism. Therefore, our data extend to kinesin-2 the two-water ATP hydrolysis mechanism and further suggest that it is universal within the kinesin superfamily

A compact viral processing proteinase/ubiquitin hydrolase from the OTU family.

International audienceTurnip yellow mosaic virus (TYMV)--a member of the alphavirus-like supergroup of viruses--serves as a model system for positive-stranded RNA virus membrane-bound replication. TYMV encodes a precursor replication polyprotein that is processed by the endoproteolytic activity of its internal cysteine proteinase domain (PRO). We recently reported that PRO is actually a multifunctional enzyme with a specific ubiquitin hydrolase (DUB) activity that contributes to viral infectivity. Here, we report the crystal structure of the 150-residue PRO. Strikingly, PRO displays no homology to other processing proteinases from positive-stranded RNA viruses, including that of alphaviruses. Instead, the closest structural homologs of PRO are DUBs from the Ovarian tumor (OTU) family. In the crystal, one molecule's C-terminus inserts into the catalytic cleft of the next, providing a view of the N-terminal product complex in replication polyprotein processing. This allows us to locate the specificity determinants of PRO for its proteinase substrates. In addition to the catalytic cleft, at the exit of which the active site is unusually pared down and solvent-exposed, a key element in molecular recognition by PRO is a lobe N-terminal to the catalytic domain. Docking models and the activities of PRO and PRO mutants in a deubiquitylating assay suggest that this N-terminal lobe is also likely involved in PRO's DUB function. Our data thus establish that DUBs can evolve to specifically hydrolyze both iso- and endopeptide bonds with different sequences. This is achieved by the use of multiple specificity determinants, as recognition of substrate patches distant from the cleavage sites allows a relaxed specificity of PRO at the sites themselves. Our results thus shed light on how such a compact protein achieves a diversity of key functions in viral genome replication and host-pathogen interaction

The Ubiquitin-Proteasome System Regulates the Accumulation of Turnip yellow mosaic virus RNA-Dependent RNA Polymerase during Viral Infection[W]

Replication of positive-strand RNA viruses, the largest group of plant viruses, is initiated by viral RNA-dependent RNA polymerase (RdRp). This work shows that Turnip yellow mosaic virus RdRp is a target of the ubiquitin-proteasome system in plant cells during viral infection and supports the idea that proteasomal degradation may constitute another level of regulation of viral replication

Structural plasticity of the N-terminal capping helix of the TPR domain of kinesin light chain.

Kinesin1 plays a major role in neuronal transport by recruiting many different cargos through its kinesin light chain (KLC). Various structurally unrelated cargos interact with the conserved tetratricopeptide repeat (TPR) domain of KLC. The N-terminal capping helix of the TPR domain exhibits an atypical sequence and structural features that may contribute to the versatility of the TPR domain to bind different cargos. We determined crystal structures of the TPR domain of both KLC1 and KLC2 encompassing the N-terminal capping helix and show that this helix exhibits two distinct and defined orientations relative to the rest of the TPR domain. Such a difference in orientation gives rise, at the N-terminal part of the groove, to the formation of one hydrophobic pocket, as well as to electrostatic variations at the groove surface. We present a comprehensive structural analysis of available KLC1/2-TPR domain structures that highlights that ligand binding into the groove can be specific of one or the other N-terminal capping helix orientations. Further, structural analysis reveals that the N-terminal capping helix is always involved in crystal packing contacts, especially in a TPR1:TPR1' contact which highlights its propensity to be a protein-protein interaction site. Together, these results underline that the structural plasticity of the N-terminal capping helix might represent a structural determinant for TPR domain structural versatility in cargo binding