Biology subjects

Kato, T.

Publications and source records attributed to Kato, T..

85 records · Page 5Linked to original sources

bioRxiv2021

Elucidation of fibril structure responsible for swimming in Spiroplasma using electron microscopy

Spiroplasma, which are known pathogens and commensals of arthropods and plants, are helical-shaped bacteria that lack a peptidoglycan layer. Spiroplasma swim by alternating between left- and right-handed helicity. Of note, this system is not related to flagellar motility, which is widespread in bacteria. A helical ribbon running along the inner side of the helical cell should be responsible for cell helicity and comprises the bacterial actin homolog, MreB, and a protein specific to Spiroplasma, fibril. Here, we isolated the ribbon and its major component, fibril filament, for electron microscopy (EM) analysis. Single-particle analysis of the fibril filaments using the negative-staining EM revealed a three-dimensional chain structure composed of rings with a size of 11 nm wide and 6 nm long, connected by a backbone cylinder with an 8.7 nm interval with a twist along the filament axis. This structure was verified through EM tomography of quick-freeze deep-etch replica sample, with a focus on its handedness. The handedness and pitch of the helix for the isolated ribbon and fibril filament agreed with those of the cell in the resting state. Structures corresponding to the alternative state were not identified. These results suggest that the helical cell structure is supported by fibril filaments; however, the helical switch is caused by the force generated by the MreB proteins. The isolation and structural outline of the fibril filaments provide crucial information for an in-depth clarification of the unique swimming mechanism of Spiroplasma.

microbiology↗

bioRxiv2020

Structure of the molecular bushing of the bacterial flagellar motor

The bacterial flagellum is a motility organelle, consisting of the basal body acting as a rotary motor, the filament as a helical propeller and the hook connecting these two as a universal joint1,2. The basal body contains three rings: the MS ring as the transmembrane core of the rotor; the C ring essential for torque generation and switching regulation; and the LP ring as a bushing supporting the distal rod for its rapid, stable rotation without much friction. The negatively charged surface of the distal rod suggested electrostatic repulsive force in supporting high-speed rotation of the rod as a drive shaft3, but the LP ring structure was needed to see the actual mechanisms of its bushing function and assembly against the repulsive force. Here we report the LP ring structure by electron cryomicroscopy at 3.5 [A] resolution, showing 26-fold rotational symmetry and intricate intersubunit interactions of each subunit with up to six partners that explains the structural stability. The inner surface is charged both positively and negatively, and positive charges on the P ring presumably play important roles in its initial assembly around the rod in the peptidoglycan layer followed by the L ring assembly in the outer membrane.

molecular biology↗

bioRxiv2020

Native structure of flagellar MS ring is formed by 34 subunits with 23-fold and 11-fold subsymmetries

The bacterial flagellar MS ring is a transmembrane complex acting as the core of the flagellar motor. It not only acts as the template for rod and C ring assembly but also houses the type III protein export gate for assembly of the rod, hook and filament. The cytoplasmic C ring, involved in torque generation and rotation switch, is directly attached to the MS ring, and a symmetry mismatch between 26-fold MS ring and 34-fold C ring had been a long puzzle as to whether this would play some role in motor function. Although this puzzle seemed to have been resolved by the recent high-resolution structure of the MS ring with 33-fold symmetry with a variation from 32-fold to 35-fold because the C ring also shows a similar symmetry variation, it still remained ambiguous whether their symmetries are matched in the native motor structure. Here we show that the native MS ring structure formed by full-length FliF is 34-fold with no symmetry variation whereas the C ring has a small symmetry variation, indicating a flexibility in C ring assembly to generate small symmetry mismatches. We also show two conformations of FliF in part of its periplasmic region to form the 34-subunit ring with 23-fold and 11-fold subsymmetries in the inner and middle M ring, respectively, to accommodate the export gate at the center of the M ring.

microbiology↗

bioRxiv2020

MafF is an anti-viral host factor that suppresses transcription from Hepatitis B Virus and Epstein Barr Virus promoters

Hepatitis B Virus (HBV) is a stealth virus that exhibits only minimal induction of the interferon system that is required for both innate and adaptive immune responses. However, 90% of acutely infected adults can clear the virus, suggesting the presence of additional mechanisms that facilitate viral clearance. Herein, we report that Maf bZIP transcription factor F (MafF) promotes host defense against infection with HBV. Using siRNA library and an HBV/NL reporter virus, we screened to identify anti-HBV host factors. Our data showed that silencing of MafF led to a 6-fold increase in luciferase activity after HBV/NL infection. Overexpression of MafF reduced HBV core promoter transcriptional activity, which was relieved upon mutating the putative MafF binding region. Loss of MafF expression by CRISPR/CAS9 (in HepG2-hNTCP-C4 cells) or siRNA silencing (in primary hepatocytes [PXB]), induced HBV core and HBV pregenomic RNA (pgRNA) levels, respectively, after HBV infection. MafF physically binds to HBV core promoter and competitively inhibits HNF-4 binding to an overlapping sequence in HBV enhancer II sequence (EnhII) as seen by ChIP analysis. MafF expression was induced by IL-1{beta}/TNF- treatment in both HepG2 and PXB cells, in an NF-{kappa}B-dependent manner. Consistently, MafF expression levels were significantly enhanced and positively correlated with the levels of these cytokines in patients with chronic HBV infection, especially in the immune clearance phase. ImportanceHBV is a leading cause of chronic liver diseases, infecting about 250 million people worldwide. HBV has developed strategies to escape interferon-dependent innate immune responses. Hence, the identification of other anti-HBV mechanisms is important for understanding HBV pathogenesis, and developing anti-HBV strategies. MafF was shown to suppress transcription from HBV core promoter, leading to a significant suppression of HBV life cycle. Furthermore, MafF expression was induced in chronic HBV patients and in primary human hepatocytes (PXB). This induction correlated with the levels of inflammatory cytokines (IL-1{beta} and TNF-). These data suggest that the induction of MafF contributes to the hosts antiviral defense by suppressing transcription from selected viral promoters. Our data shed light on a novel role for MafF as anti-HBV host restriction factor.

microbiology↗

bioRxiv2020

Promoter activity-based case-control association study on SLC6A4 highlighting hypermethylation and altered amygdala volume in male patients with schizophrenia

Associations between altered DNA methylation of the serotonin transporter (5-HTT)-encoding gene SLC6A4 and early life adversity, mood and anxiety disorders, and amygdala reactivity have been reported. However, few studies have examined epigenetic alterations of SLC6A4 in schizophrenia (SZ). We examined CpG sites of SLC6A4, whose DNA methylation levels have been reported to be altered in bipolar disorder, using three independent cohorts of patients with SZ and age-matched controls. We found significant hypermethylation of a CpG site in SLC6A4 in male patients with SZ in all three cohorts. We showed that chronic administration of risperidone did not affect the DNA methylation status at this CpG site using common marmosets, and that in vitro DNA methylation at this CpG site diminished the promoter activity of SLC6A4. We then genotyped the 5-HTT-linked polymorphic region (5-HTTLPR) and investigated the relationship among 5-HTTLPR, DNA methylation, and amygdala volume using brain imaging data. We found that patients harboring low-activity 5-HTTLPR alleles showed hypermethylation and they showed a negative correlation between DNA methylation levels and left amygdala volumes. These results suggest that hypermethylation of the CpG site in SLC6A4 is involved in the pathophysiology of SZ, especially in male patients harboring low-activity 5-HTTLPR alleles.

genetics↗

bioRxiv2020

Structural basis of ethnic-specific variants of PAX4 associated with type 2 diabetes

Recently, we conducted genome-wide association studies of type 2 diabetes (T2D) in a Japanese population, which identified 20 novel T2D loci that were not associated with T2D in Europeans. Moreover, nine novel missense risk variants, such as those of PAX4, were not rare in the Japanese population, but rare in Europeans. We report in silico structural analysis of ethnic-specific variants of PAX4, which suggests the pathogenic effect of these variants.

genetics↗

bioRxiv2020

Sub-3 A resolution structure of apoferritin using a multi-purpose TEM with a side-entry cryo-holder

The structural analysis of protein complexes by cryo-electron microscopy (cryo-EM) single particle analysis (SPA) has had great impact as a biophysical method in recent years. Many results of cryo-EM SPA are based on state-of-the-art cryo-electron microscopes customized for SPA. These are currently only available in limited locations around the world, where securing machine time is highly competitive. One potential solution for this time-competitive situation is to reuse existing multi-purpose equipment. Here, we used a multi-purpose TEM with a side entry cryo-holder at our facility to evaluate the potential of high-resolution SPA. We report a 3 [A] resolution map of apoferritin with local resolution extending to 2.6 [A]. The map clearly showed two positions of an aromatic side chain. We also verified the optimal imaging conditions depending on different electron microscope and camera combinations. This study demonstrates the possibilities of more widely available and established electron microscopes, and their applications for cryo-EM SPA.

molecular biology↗

bioRxiv2020

Extraction of Protein Dynamics Information Hidden in Cryo-EM Map Using Deep Learning

Technical breakthroughs in cryogenic electron microscopy (cryo-EM)-based single-particle analysis have enabled the structures of numerous proteins to be solved at atomic or near-atomic resolutions, including extremely large macromolecules whose structures could not be solved by conventional techniques. Determining the dynamics properties of these macromolecules, based on their solved structures, can further improve our understanding of their functional mechanisms. However, such analysis is often hampered by the large molecular size and complex structural assembly, making both experimental and computational approaches to determine dynamics properties challenging. Here, we report a deep learning-based approach, DEFMap, to extract the dynamics information "hidden" in cryo-EM density maps. By relying only on cryo-EM maps, DEFMap successfully provided dynamics information equivalent to that determined from molecular dynamics (MD) simulations and experimental approaches at the atomic and residue levels. Additionally, DEFMap could detect dynamics changes associated with molecular recognition and the accompanying allosteric conformational stabilizations, which trigger various biological events such as signal transduction and enzyme catalysis. This approach will provide new insights into the functional mechanisms of biological molecules, accelerating modern molecular biology researches. Furthermore, this advanced strategy combining experimental data, deep learning approaches, and MD simulations would open a new multidisciplinary science area

molecular biology↗

bioRxiv2020

The mechanical inhibition of the isolated Vo from V-ATPase for proton conductance

V-ATPase is an energy converting enzyme, coupling ATP hydrolysis/synthesis in the hydrophilic V1 moiety, with proton flow through the Vo membrane moiety, via rotation of the central rotor complex relative to the surrounding stator apparatus. Upon dissociation from the V1 domain, the Vo of eukaryotic V-ATPase can adopt a physiologically relevant auto-inhibited form in which proton conductance through the Vo is prevented, however the molecular mechanism of this inhibition is not fully understood. Using cryo-electron microscopy, we determined the structure of both the holo V/A-ATPase and the isolated Vo at near-atomic resolution, respectively. These structures clarify how the isolated Vo adopts the auto-inhibited form and how the holo complex prevents the formation of this inhibited Vo form. One Sentence SummaryCryo-EM structures of rotary V-ATPase reveal the ON-OFF switching mechanism of H+ translocation in the Vo membrane domain.

biophysics↗

bioRxiv2020

Understanding Adaptive Immune System as Reinforcement Learning

The adaptive immune system of vertebrates can detect, respond to, and memorize diverse pathogens from past experience. While the selection of T helper (Th) clones is the simple and established mechanism to recognize and memorize new pathogens, the question that still remains unexplored is how the Th cells can acquire better ways to bias the responses of immune cells for eliminating pathogens more efficiently by translating the recognized antigen information into regulatory signals. In this work, we address this problem by associating the adaptive immune network organized by the Th cells with reinforcement learning (RL). By employing recent advancements of network-based RL, we show that the Th immune network can acquire the association between antigen patterns of and the effective responses to pathogens. Moreover, the clonal selection as well as other inter-cellular interactions are derived as a learning rule of this network. We also demonstrate that the stationary clone-size distribution after learning shares characteristic features with those observed experimentally. Our theoretical framework may contribute to revising and renewing our understanding of adaptive immunity as a learning system.

systems biology↗

bioRxiv2019

Refined mechanism of Mycoplasma mobile gliding based on structure, ATPase activity, and sialic acid binding of machinery

Mycoplasma mobile, a fish pathogen, glides on solid surfaces by repeated catch, pull, and release of sialylated oligosaccharides by a unique mechanism based on ATP energy. The gliding machinery is composed of huge surface proteins and an internal jellyfish -like structure. Here, we elucidated the detailed three-dimensional structures of the machinery by electron cryotomography. The internal tentacle -like structure hydrolyzed ATP, which was consistent with the fact that the paralogs of the - and {beta}-subunits of F1-ATPase are at the tentacle structure. The electron microscopy suggested conformational changes of the tentacle structure depending on the presence of ATP analogs. The gliding machinery was isolated and shown that the binding activity to sialylated oligosaccharide was higher in the presence of ADP than in the presence of ATP. Based on these results, we proposed a model to explain the mechanism of M. mobile gliding.\n\nIMPORTANCEThe genus Mycoplasma is made up of the smallest parasitic and sometimes commensal bacteria; Mycoplasma pneumoniae, which causes human walking pneumonia, is representative. More than ten Mycoplasma species glide on host tissues by novel mechanisms always in the direction of the distal side of the machinery. Mycoplasma mobile, the fastest species in the genus, catches, pulls, and releases sialylated oligosaccharides (SOs), the carbohydrate molecules also targeted by influenza viruses, by means of a specific receptor and using ATP hydrolysis for energy. Here, the architecture of the gliding machinery was visualized three-dimensionally by electron cryotomography (ECT), and changes in the structure and binding activity coupled to ATP hydrolysis were discovered. Based on the results, a refined mechanism was proposed for this unique motility.

microbiology↗

bioRxiv2019

Structure of the native supercoiled flagellar hook as a universal joint

Bacteria swim in viscous liquid environments by using the flagellum1-3. The flagellum is composed of about 30 different proteins and can be roughly divided into three parts: the basal body, the hook and the filament. The basal body acts as a rotary motor powered by ion motive force across the cytoplasmic membrane as well as a protein export apparatus to construct the axial structure of the flagellum. The filament is as a helical propeller, and it is a supercoiled form of a helical tubular assembly consisting of a few tens of thousands of flagellin molecules4. The hook is a relatively short axial segment working as a universal joint connecting the basal body and the filament for smooth transmission of motor torque to the filament5,6. The structure of hook has been studied by combining X-ray crystal structure of a core fragment of hook protein FlgE and electron cryomicroscopy (cryoEM) helical image analysis of the polyhook in the straight form and has given a deep insight into the universal joint mechanism7. However, the supercoiled structure of the hook was an approximate model based on the atomic model of the straight hook without its inner core domain7 and EM observations of supercoiled polyhook by freeze-dry and Pt/Pd shadow cast8. Here we report the native supercoiled hook structure at 3.1 [A] resolution by cryoEM single particle image analysis of the polyhook. The atomic model built on the three-dimensional (3D) density map show the actual changes in subunit conformation and intersubunit interactions upon compression and extension of the 11 protofilaments that occur during their smoke ring-like rotation and allow the hook to function as a dynamic molecular universal joint with high bending flexibility and twisting rigidity.

biophysics↗

bioRxiv2018

Characteristic Localization of Neuronatin in Rat Tissues

Neuronatin (Nnat) is expressed in the pituitary, pancreas, and other tissues; however, the function of NNAT is still unclear. Recent studies have demonstrated that NNAT is localized in the sex determining region Y-box 2-positive stem/progenitor cells in the developing rat pituitary primordium and is downregulated during differentiation into mature hormone-producing cells. Moreover, NNAT is widely localized in subcellular organelles, excluding the Golgi. Here, we further evaluated NNAT expression and intracellular localization in embryonic and postnatal rat tissues such as the pancreas, tongue, whisker hair follicle, and testis. Immunohistochemistry showed that NNAT was localized in undifferentiated cells (i.e., epithelial basal cells and basement cells in the papillae of the tongue and round and elongated spermatids of the testis) as well as in differentiated cells (insulin-positive cells and exocrine cells of the pancreas, taste receptor cells of the fungiform papilla, the inner root sheath of whisker hair follicles, and spermatozoa). Additionally, NNAT showed novel intracellular localization in acrosomes in the spermatozoa. Because the endoplasmic reticulum (ER) is excluded from spermatozoa and sarco/ER Ca2+-ATPase isoform 2 (SERCA2) is absent from the inner root sheath, these findings suggested that NNAT localization in the ER and its interaction with SERCA2 were cell-or tissue-specific properties.

developmental biology↗