N-terminal region of Drosophila melanogaster Argonaute2 forms amyloid-like aggregates.

BACKGROUND: Argonaute proteins play a central role in RNA silencing by forming protein-small RNA complexes responsible for the silencing process. While most Argonaute proteins have a short N-terminal region, Argonaute2 in Drosophila melanogaster (DmAgo2) harbors a long and unique N-terminal region. Previous in vitro biochemical studies have shown that the loss of this region does not impair the RNA silencing activity of the complex. However, an N-terminal mutant of Drosophila melanogaster has demonstrated abnormal RNA silencing activity. To explore the causes of this discrepancy between in vitro and in vivo studies, we investigated the biophysical properties of the region. The N-terminal region is highly rich in glutamine and glycine residues, which is a well-known property for prion-like domains, a subclass of amyloid-forming peptides. Therefore, the possibility of the N-terminal region functioning as an amyloid was tested. RESULTS: Our in silico and biochemical assays demonstrated that the N-terminal region exhibits amyloid-specific properties. The region indeed formed aggregates that were not dissociated even in the presence of sodium dodecyl sulfate. Also, the aggregates enhanced the fluorescence intensity of thioflavin-T, an amyloid detection reagent. The kinetics of the aggregation followed that of typical amyloid formation exhibiting self-propagating activity. Furthermore, we directly visualized the aggregation process of the N-terminal region under fluorescence microscopy and found that the aggregations took fractal or fibril shapes. Together, the results indicate that the N-terminal region can form amyloid-like aggregates. CONCLUSIONS: Many other amyloid-forming peptides have been reported to modulate the function of proteins through their aggregation. Therefore, our findings raise the possibility that aggregation of the N-terminal region regulates the RNA silencing activity of DmAgo2.

Real-time observation of flexible domain movements in CRISPR-Cas9.

The CRISPR-associated protein Cas9 is widely used for genome editing because it cleaves target DNA through the assistance of a single-guide RNA (sgRNA). Structural studies have revealed the multi-domain architecture of Cas9 and suggested sequential domain movements of Cas9 upon binding to the sgRNA and the target DNA These studies also hinted at the flexibility between domains; however, it remains unclear whether these flexible movements occur in solution. Here, we directly observed dynamic fluctuations of multiple Cas9 domains, using single-molecule FRET We found that the flexible domain movements allow Cas9 to adopt transient conformations beyond those captured in the crystal structures. Importantly, the HNH nuclease domain only accessed the DNA cleavage position during such flexible movements, suggesting the importance of this flexibility in the DNA cleavage process. Our FRET data also revealed the conformational flexibility of apo-Cas9, which may play a role in the assembly with the sgRNA Collectively, our results highlight the potential role of domain fluctuations in driving Cas9-catalyzed DNA cleavage.

How Cytoplasmic Dynein Couples ATP Hydrolysis Cycle to Diverse Stepping Motions: Kinetic Modeling.

Cytoplasmic dynein is a two-headed molecular motor that moves to the minus end of a microtubule by ATP hydrolysis free energy. By employing its two heads (motor domains), cytoplasmic dynein exhibits various bipedal stepping motions: inchworm and hand-over-hand motions, as well as nonalternating steps of one head. However, the molecular basis to achieve such diverse stepping manners remains unclear because of the lack of an experimental method to observe stepping and the ATPase reaction of dynein simultaneously. Here, we propose a kinetic model for bipedal motions of cytoplasmic dynein and perform Gillespie Monte Carlo simulations that qualitatively reproduce most experimental data obtained to date. The model represents the status of each motor domain as five states according to conformation and nucleotide- and microtubule-binding conditions of the domain. In addition, the relative positions of the two domains were approximated by three discrete states. Accompanied by ATP hydrolysis cycles, the model dynein stochastically and processively moved forward in multiple steps via diverse pathways, including inchworm and hand-over-hand motions, similarly to experimental data. The model reproduced key experimental motility-related properties, including velocity and run length, as functions of the ATP concentration and external force, therefore providing a plausible explanation of how dynein achieves various stepping manners with explicit characterization of nucleotide states. Our model highlights the uniqueness of dynein in the coupling of ATPase with its movement during both inchworm and hand-over-hand stepping.

The extracellular loop of pendrin and prestin modulates their voltage-sensing property.

Pendrin and prestin belong to the solute carrier 26 (SLC26) family of anion transporters. Prestin is unique among the SLC26 family members in that it displays voltage-driven motor activity (electromotility) and concurrent gating currents that manifest as nonlinear cell membrane electrical capacitance (nonlinear capacitance (NLC)). Although the anion transport mechanism of the SLC26 proteins has begun to be elucidated, the molecular mechanism of electromotility, which is thought to have evolved from an ancestral ion transport mechanism, still remains largely elusive. Here, we demonstrate that pendrin also exhibits large NLC and that charged residues present in one of the extracellular loops of pendrin and prestin play significant roles in setting the voltage-operating points of NLC. Our results suggest that the molecular mechanism responsible for sensing voltage is not unique to prestin among the members of the SLC26 family and that this voltage-sensing mechanism works independently of the anion transport mechanism.

The 2.8 Å crystal structure of the dynein motor domain.

Dyneins are microtubule-based AAA(+) motor complexes that power ciliary beating, cell division, cell migration and intracellular transport. Here we report the most complete structure obtained so far, to our knowledge, of the 380-kDa motor domain of Dictyostelium discoideum cytoplasmic dynein at 2.8 Å resolution; the data are reliable enough to discuss the structure and mechanism at the level of individual amino acid residues. Features that can be clearly visualized at this resolution include the coordination of ADP in each of four distinct nucleotide-binding sites in the ring-shaped AAA(+) ATPase unit, a newly identified interaction interface between the ring and mechanical linker, and junctional structures between the ring and microtubule-binding stalk, all of which should be critical for the mechanism of dynein motility. We also identify a long-range allosteric communication pathway between the primary ATPase and the microtubule-binding sites. Our work provides a framework for understanding the mechanism of dynein-based motility.

Preference of CAMSAP3 for expanded microtubule lattice contributes to stabilization of the minus end.

CAMSAPs are proteins that show microtubule minus-end-specific localization, decoration, and stabilization. Although the mechanism for minus-end recognition via their C-terminal CKK domain has been well described in recent studies, it is unclear how CAMSAPs stabilize microtubules. Our several binding assays revealed that the D2 region of CAMSAP3 specifically binds to microtubules with the expanded lattice. To investigate the relationship between this preference and the stabilization effect of CAMSAP3, we precisely measured individual microtubule lengths and found that D2 binding expanded the microtubule lattice by ∼3%. Consistent with the notion that the expanded lattice is a common feature of stable microtubules, the presence of D2 slowed the microtubule depolymerization rate to ∼1/20, suggesting that the D2-triggered lattice expansion stabilizes microtubules. Combining these results, we propose that CAMSAP3 stabilizes microtubules by lattice expansion upon D2 binding, which further accelerates the recruitment of other CAMSAP3 molecules. Because only CAMSAP3 has D2 and the highest microtubule-stabilizing effect among mammalian CAMSAPs, our model also explains the molecular basis for the functional diversity of CAMSAP family members.

Accumulation of TERT in mitochondria exerts two opposing effects on apoptosis.

Telomerase reverse transcriptase (TERT) is a protein that catalyzes the reverse transcription of telomere elongation. TERT is also expected to play a non-canonical role beyond telomere lengthening since it localizes not only in the nucleus but also in mitochondria, where telomeres do not exist. Several studies have reported that mitochondrial TERT regulates apoptosis induced by oxidative stress. However, there is still some controversy as to whether mitochondrial TERT promotes or inhibits apoptosis, mainly due to the lack of information on changes in TERT distribution in individual cells over time. Here, we simultaneously detected apoptosis and TERT localization after oxidative stress in individual HeLa cells by live-cell tracking. Single-cell tracking revealed that the stress-induced accumulation of TERT in mitochondria caused apoptosis, but that accumulation increased over time until cell death. The results suggest a new model in which mitochondrial TERT has two opposing effects at different stages of apoptosis: it predetermines apoptosis at the first stage of cell-fate determination, but also delays apoptosis at the second stage. As such, our data support a model that integrates the two opposing hypotheses on mitochondrial TERT's effect on apoptosis. Furthermore, detailed statistical analysis of TERT mutations, which have been predicted to inhibit TERT transport to mitochondria, revealed that these mutations suppress apoptosis independent of mitochondrial localization of TERT. Together, these results imply that the non-canonical functions of TERT affect a wide range of mitochondria-dependent and mitochondria-independent apoptosis pathways.

Biomolecular-motor-based nano- or microscale particle translocations on DNA microarrays.

We aimed to create autonomous on-chip systems that perform targeted translocations of nano- or microscale particles in parallel using machinery that mimics biological systems. By exploiting biomolecular-motor-based motility and DNA hybridization, we demonstrate that single-stranded DNA-labeled microtubules gliding on kinesin-coated surfaces acted as cargo translocators and that single-stranded DNA-labeled cargoes were loaded/unloaded onto/from gliding microtubules at micropatterned loading/unloading sites specified by DNA base sequences. Our results will help to create autonomous molecular sorters and sensors.

In Vitro Reconstitution of Dynein Force Exertion in a Bulk Viscous Medium.

The forces generated by microtubules (MTs) and their associated motors orchestrate essential cellular processes ranging from vesicular trafficking to centrosome positioning [1, 2]. To date, most studies have focused on MT force exertion by motors anchored to a static surface, such as the cell cortex in vivo or glass surfaces in vitro [2-4]. However, motors also transport large cargos and endomembrane networks, whose hydrodynamic interactions with the viscous cytoplasm should generate sizable forces in bulk. Such forces may contribute to MT aster centration, organization, and orientation [5-14] but have yet to be evidenced and studied in a minimal reconstituted system. By developing a bulk motility assay, based on stabilized MTs and dynein-coated beads freely floating in a viscous medium away from any surface, we demonstrate that the motion of a cargo exerts a pulling force on the MT and propels it in opposite direction. Quantification of resulting MT movements for different motors, motor velocities, over a range of cargo sizes and medium viscosities shows that the efficiency of this mechanism is primarily determined by cargo size and MT length. Forces exerted by cargos are additive, allowing us to recapitulate tug-of-war situations or bi-dimensional motions of minimal asters. These data also reveal unappreciated effects of the nature of viscous crowders and hydrodynamic interactions between cargos and MTs, likely relevant to understand this mode of force exertion in living cells. This study reinforces the notion that endomembrane transport can exert significant forces on MTs.

Small stepping motion of processive dynein revealed by load-free high-speed single-particle tracking.

Cytoplasmic dynein is a dimeric motor protein which processively moves along microtubule. Its motor domain (head) hydrolyzes ATP and induces conformational changes of linker, stalk, and microtubule binding domain (MTBD) to trigger stepping motion. Here we applied scattering imaging of gold nanoparticle (AuNP) to visualize load-free stepping motion of processive dynein. We observed artificially-dimerized chimeric dynein, which has the head, linker, and stalk from Dictyostelium discoideum cytoplasmic dynein and the MTBD from human axonemal dynein, whose structure has been well-studied by cryo-electron microscopy. One head of a dimer was labeled with 30 nm AuNP, and stepping motions were observed with 100 µs time resolution and sub-nanometer localization precision at physiologically-relevant 1 mM ATP. We found 8 nm forward and backward steps and 5 nm side steps, consistent with on- and off-axes pitches of binding cleft between αß-tubulin dimers on the microtubule. Probability of the forward step was 1.8 times higher than that of the backward step, and similar to those of the side steps. One-head bound states were not clearly observed, and the steps were limited by a single rate constant. Our results indicate dynein mainly moves with biased small stepping motion in which only backward steps are slightly suppressed.

Long-term efficacy and safety of secukinumab in Japanese patients with moderate to severe plaque psoriasis: 3-year results of a double-blind extension study.

Secukinumab, a fully human monoclonal antibody neutralizing interleukin-17A, has been shown to have significant efficacy in the treatment of moderate to severe psoriasis. Long-term (3-year) efficacy and safety of secukinumab in Japanese patients with moderate to severe psoriasis were evaluated in an extension study of a large phase 3 global study (SCULPTURE). In the core study, 52 Japanese patients with 75% improvement of Psoriasis Area and Severity Index (PASI-75) response at week 12 were re-randomized to a fixed interval (FI; every 4 weeks) schedule and retreatment as needed (RAN), in which patients received placebo until start of relapse, at which time secukinumab was reinitiated. Fifty Japanese patients completed the 52-week core study, and 47 patients entered the extension study with the same double-blind regimens up to week 152. All patients in the secukinumab 300 mg FI and seven patients in 150 mg FI groups completed 3 years of treatment. PASI-90 and -100 at the end of year 3 were achieved in 69.2% and 53.8%, respectively, in 300 mg FI and 42.9% and 42.9%, respectively, in 150 mg FI, indicating high sustained response in 300 mg FI. Mean absolute PASI was continually low in 300 mg FI and numerically higher in 150 mg FI. Dermatology Life Quality Index of 0/1 was maintained by approximately two-thirds of 300 mg FI patients, and all EuroQoL 5-Dimension Health Questionnaire domain measures were also improved. FI dosing was consistently more efficacious than RAN. The safety profile of secukinumab remained favorable, with no new safety concerns identified.

Second harmonic generation polarization microscopy as a tool for protein structure analysis.

Cryo-electron microscopy and X-ray crystallography have been the major tools of protein structure analysis for decades and will certainly continue to be essential in the future. Moreover, nuclear magnetic resonance or Förster resonance energy transfer can measure structural dynamics. Here, we propose to add optical second-harmonic generation (SHG), which is a nonlinear optical scattering process sensitive to molecular structures in illuminated materials, to the tool-kit of structural analysis methodologies. SHG can be expected to probe the structural changes of proteins in the physiological condition, and thus link protein structure and biological function. We demonstrate that a conformational change as well as its dynamics in protein macromolecular assemblies can be detected by means of SHG polarization measurement. To prove the capability of SHG polarization measurement with regard to protein structure analysis, we developed an SHG polarization microscope to analyze microtubules in solution. The difference in conformation between microtubules with different binding molecules was successfully observed as polarization dependence of SHG intensity. We also succeeded in capturing the temporal variation of structure in a photo-switchable protein crystal in both activation and inactivation processes. These results illustrate the potential of this method for protein structure analysis in physiological solutions at room temperature without any labeling.

Kinesin-binding-triggered conformation switching of microtubules contributes to polarized transport.

Kinesin-1, the founding member of the kinesin superfamily of proteins, is known to use only a subset of microtubules for transport in living cells. This biased use of microtubules is proposed as the guidance cue for polarized transport in neurons, but the underlying mechanisms are still poorly understood. Here, we report that kinesin-1 binding changes the microtubule lattice and promotes further kinesin-1 binding. This high-affinity state requires the binding of kinesin-1 in the nucleotide-free state. Microtubules return to the initial low-affinity state by washing out the binding kinesin-1 or by the binding of non-hydrolyzable ATP analogue AMPPNP to kinesin-1. X-ray fiber diffraction, fluorescence speckle microscopy, and second-harmonic generation microscopy, as well as cryo-EM, collectively demonstrated that the binding of nucleotide-free kinesin-1 to GDP microtubules changes the conformation of the GDP microtubule to a conformation resembling the GTP microtubule.

Efficacy and safety of secukinumab in patients with generalized pustular psoriasis: A 52-week analysis from phase III open-label multicenter Japanese study.

Generalized pustular psoriasis (GPP) is a severe inflammatory skin disease characterized by the presence of sterile pustules covering almost the entire body and systemic symptoms such as fever. Secukinumab, a fully human-recombinant anti-interleukin-17A monoclonal antibody was indicated for psoriasis vulgaris and psoriatic arthritis in Japan but is not yet investigated for GPP. In this phase III, open-label multicenter single arm study, the efficacy and safety of secukinumab as monotherapy or with co-medication was evaluated in 12 Japanese patients with GPP. All the patients received secukinumab 150 mg s.c. at baseline, week 1, 2, 3 and 4, and then every 4 weeks. Two non-responders were up-titrated to 300 mg. Change in GPP severity from baseline was evaluated by clinical global impression (CGI) categorized as "worsened", "no change", "minimally improved", "much improved" or "very much improved". Treatment success was achieved by 83.3% (n = 10) of patients at week 16 (primary end-point) with CGI evaluated as "very much improved" (n = 9) and "much improved" (n = 1). Moreover, the area of erythema with pustules improved as early as week 1 and resolved by week 16 in most of the patients. The improvements were sustained throughout 52 weeks. Over the 52-week treatment period, secukinumab was well tolerated with no unexpected safety signals. Nasopharyngitis, urticaria, diabetes mellitus and arthralgia were the frequent adverse events reported. The data from this study shows that secukinumab can become one of the potent treatment options for GPP.

Compact and stable SNAP ligand-conjugated quantum dots as a fluorescent probe for single-molecule imaging of dynein motor protein.

Compact SNAP ligand-conjugated quantum dots (<10 nm) with high colloidal stability over a wide range of pH (5-9) have been synthesized as fluorescent probe for the single-molecule imaging of dynein motor protein.

Direct observation shows superposition and large scale flexibility within cytoplasmic dynein motors moving along microtubules.

Cytoplasmic dynein is a dimeric AAA(+) motor protein that performs critical roles in eukaryotic cells by moving along microtubules using ATP. Here using cryo-electron microscopy we directly observe the structure of Dictyostelium discoideum dynein dimers on microtubules at near-physiological ATP concentrations. They display remarkable flexibility at a hinge close to the microtubule binding domain (the stalkhead) producing a wide range of head positions. About half the molecules have the two heads separated from one another, with both leading and trailing motors attached to the microtubule. The other half have the two heads and stalks closely superposed in a front-to-back arrangement of the AAA(+) rings, suggesting specific contact between the heads. All stalks point towards the microtubule minus end. Mean stalk angles depend on the separation between their stalkheads, which allows estimation of inter-head tension. These findings provide a structural framework for understanding dynein's directionality and unusual stepping behaviour.

The γ-tubulin-specific inhibitor gatastatin reveals temporal requirements of microtubule nucleation during the cell cycle.

Inhibitors of microtubule (MT) assembly or dynamics that target α/ß-tubulin are widely exploited in cancer therapy and biological research. However, specific inhibitors of the MT nucleator γ-tubulin that would allow testing temporal functions of γ-tubulin during the cell cycle are yet to be identified. By evolving ß-tubulin-binding drugs we now find that the glaziovianin A derivative gatastatin is a γ-tubulin-specific inhibitor. Gatastatin decreased interphase MT dynamics of human cells without affecting MT number. Gatastatin inhibited assembly of the mitotic spindle in prometaphase. Addition of gatastatin to preformed metaphase spindles altered MT dynamics, reduced the number of growing MTs and shortened spindle length. Furthermore, gatastatin prolonged anaphase duration by affecting anaphase spindle structure, indicating the continuous requirement of MT nucleation during mitosis. Thus, gatastatin facilitates the dissection of the role of γ-tubulin during the cell cycle and reveals the sustained role of γ-tubulin.

Secukinumab efficacy and safety in Japanese patients with moderate-to-severe plaque psoriasis: subanalysis from ERASURE, a randomized, placebo-controlled, phase 3 study.

Secukinumab, a fully human anti-IL-17A monoclonal antibody, neutralizes IL-17A, a key cytokine in the pathogenesis of psoriasis. Efficacy and safety of secukinumab was evaluated in Japanese patients with moderate-to-severe plaque psoriasis as part of a large Phase 3 global study (ERASURE). In this 52-week, double-blind study (ClinicalTrials.gov Identifier: NCT01365455, JapicCTI-111529), 87 patients from Japan (11.8% of 738 patients randomized in the overall study population) were equally randomized to receive secukinumab 300 mg or 150 mg, or placebo once weekly at baseline and at Weeks 1, 2, 3 and 4, then every 4 weeks. Co-primary endpoints (Week 12) were ≥75% improvement in psoriasis area-and-severity index (PASI 75) from baseline and a score of 0 (clear) or 1 (almost clear) on a 5-point Investigator's Global Assessment scale (IGA mod 2011 0/1) versus placebo. PASI 75 and IGA mod 2011 0/1 responses at Week 12 were superior with secukinumab 300 mg (82.8% and 55.2%, respectively) or 150 mg (86.2% and 55.2%, respectively) versus placebo (6.9% and 3.4%, respectively; P < 0.0001 for all). Greater than 90% improvement in PASI (PASI 90) was also superior with secukinumab 300 mg (62.1%) or 150 mg (55.2%) versus placebo (0.0%) at Week 12 (P < 0.0001 for both). Clinical responses were sustained up to Week 52 in the majority of patients. During a 12-week induction period, adverse event incidences were 48.3% with secukinumab 300 mg, 55.2% with 150 mg, and 41.4% with placebo. Secukinumab showed robust and sustainable efficacy in symptom reduction for moderate-to-severe plaque psoriasis in the Japanese patients.