Biology subjects

Terashima, H.

Publications and source records attributed to Terashima, H..

9 recordsLinked to original sources

bioRxiv2026

Structure of an active FlhA ring reveals allosteric coupling between substrate specificity and export engine activation

The bacterial flagellar type III secretion system transports structural subunits in a defined order to assemble the flagellum. FlhA is the core component of this nanomachine; its transmembrane domain functions as an ion-driven export engine and its cytoplasmic domain connected by a flexible linker forms a nonameric ring that controls substrate selection. The coupling mechanism of these activities has remained unclear because the transmembrane domain has resisted structural analysis. Here we identify linker deletions that autonomously activate the export gate and capture a functionally active, hook-type protein export state of the entire ring complex. Using cryo-electron microscopy, we determine the structure of the FlhA({Delta}331-347) ring at 2.73 [A] resolution. The structure shows linker-mediated docking of the cytoplasmic ring to the transmembrane ring to stabilize the entire ring while sterically excluding filament-type substrate binding. These findings reveal how the FlhA ring allosterically couples substrate specificity to ion-driven export during flagellar assembly.

microbiology↗

bioRxiv2024

Functional brain networks predicting sustained attention are not specific to perceptual modality

Sustained attention is essential for daily life and can be directed to information from different perceptual modalities including audition and vision. Recently, cognitive neuroscience has aimed to identify neural predictors of behavior that generalize across datasets. Prior work has shown strong generalization of models trained to predict individual differences in sustained attention performance from patterns of fMRI functional connectivity. However, it is an open question whether predictions of sustained attention are specific to the perceptual modality in which they are trained. In the current study we test whether connectome-based models predict performance on attention tasks performed in different modalities. We show first that a predefined network trained to predict adults visual sustained attention performance generalizes to predict auditory sustained attention performance in three independent datasets (N1=29, N2=60, N3=17). Next, we train new network models to predict performance on visual and auditory attention tasks separately. We find that functional networks are largely modality-general, with both model-unique and shared model features predicting sustained attention performance in independent datasets regardless of task modality. Results support the supposition that visual and auditory sustained attention rely on shared neural mechanisms and demonstrate robust generalizability of whole-brain functional network models of sustained attention.

neuroscience↗

bioRxiv2022

Human-like Modulation SensitivityEmerging through Optimization to Natural Sound Recognition

Natural sounds contain rich patterns of amplitude modulation (AM), which is one of the essential sound dimensions for hearing perception. The sensitivity of human hearing to AM measured by psychophysics takes diverse forms, from low-pass to high-pass, depending on the experimental conditions. Here, we address with a single framework the questions of why such patterns of AM sensitivity have emerged in the human auditory system and how they are realized by our neural mechanisms. Assuming that optimization for natural sound recognition has taken place during human evolution and development, we examined its effect on the formation of AM sensitivity by optimizing a computational model, specifically, a multi-layer (or deep) neural network, for natural sound recognition and simulating psychophysical experiments in which the models AM sensitivity was measured. Relatively higher layers in the optimized model exhibited qualitatively and quantitatively similar AM sensitivity to that of humans, even though the model was not designed to reproduce human-like AM sensitivity. The similarity of the models AM sensitivity to humans correlated with its sound recognition accuracy. Optimization of the model to degraded sounds revealed the necessity of natural AM patterns for the emergence of human-like AM sensitivity. Consistent results were observed from optimizations to two different types of natural sound. Moreover, simulated neurophysiological experiments on the same model revealed a correspondence between the model layers and the auditory brain regions that is based on the similarity of their neural AM tunings. The layers in which human-like psychophysical AM sensitivity emerged exhibited substantial neurophysiological similarity with the auditory midbrain and higher regions. These results suggest that the behavioral AM sensitivity of human hearing has emerged as a result of optimization for natural-sound recognition in the course of our evolution and/or development and that it is based on a stimulus representation encoded in the neural firing rates in the auditory midbrain and higher regions.

neuroscience↗

bioRxiv2021

Hoop-like role of the cytosolic interface helix in Vibrio PomA, an ion-conducting membrane protein, in the bacterial flagellar motor

Vibrio has a polar flagellum driven by sodium ions for swimming. The force-generating stator unit consists of PomA and PomB. PomA contains four-transmembrane regions and a cytoplasmic domain of approximately 100 residues which interacts with the rotor protein, FliG, to be important for the force generation of rotation. The three-dimensional structure of the stator shows that the cytosolic interface (CI) helix of PomA is located parallel to the inner membrane. In this study, we investigated the function of CI helix and its role as stator. Systematic proline mutagenesis showed that residues K64, F66, and M67 were important for this function. The mutant stators did not assemble around the rotor. Moreover, the growth defect caused by PomB plug deletion was suppressed by these mutations. We speculate that the mutations affect the structure of the helices extending from TM3 and TM4 and reduce the structural stability of the stator complex. This study suggests that the helices parallel to the inner membrane play important roles in various processes, such as the hoop-like function in securing the stability of the stator complex and the ion conduction pathway, which may lead to the elucidation of the ion permeation and assembly mechanism of the stator. ImportanceBacteria have a motor embedded in the membrane to rotate flagella as screw for swimming. The motor is composed rotor and stator complexes. The interaction between the rotor and stator converts the electrochemical potential gradient across the membrane into motor torque. The stator functions as an ion channel and is composed of two membrane proteins, MotA and MotB for proton or PomA and PomB for sodium ion. Based on the structural data of stator, we systematically introduce the proline replacement mutations and found that the cytosolic interface (CI) helix which is located parallel to the inner membrane between the second and third transmembrane (TM) segments, performs a hoop-like function in securing the stability of the stator complex and the ion conduction pathway. The results of this study provide novel insights into the energy conversion mechanism of the flagellar motor and the general mechanism of the ion channel function.

biophysics↗

bioRxiv2021

Function of the Vibrio PomB plug region based on the stator rotation model for bacterial flagellar motor

Bacterial flagella are the only real rotational motor organs in the biological world. The spiral-shaped flagellar filaments that extend from the cell surface rotate like a screw to create a propulsive force. The base of the flagellar filament has a protein motor consisting of a stator and a rotor embedded in the membrane. The motor part has stators composed of two types of membrane subunits, PomA(MotA) and PomB(MotB), which are energy converters coupled to the ion flow that assemble around the rotor. Recently, structures of the stator, in which two molecules of MotB stuck in the center of the MotA ring made of five molecules, were reported and a model in which the MotA ring rotates with respect to MotB, which is coupled to the influx of ions, was proposed. We focused on the Vibrio PomB plug region, which has been reported to control the activation of flagellar motors. We searched for the plug region, which is the interacting region, through site-directed photo-cross-linking and disulfide cross-linking experiments. Our results demonstrated that it interacts with the extracellular short loop region of PomA, which is between transmembrane 3 and 4. Although the motor halted following cross-linking, its function was recovered with a reducing reagent that disrupted the disulfide bond. Our results support the hypothesis, which has been inferred from the stator structure, that the plug region terminates the ion inflow by stopping the rotation of the rotor. ImportanceThe flagellar biological motor resembles a mechanical motor, which is composed of stator and rotor and where the rotational force is transmitted by gear-like movements. We hypothesized that the flagellar the rotation of stator that the pentamer of A subunits revolves around the axis of the B subunit dimer with ion flow. The plug region of the B subunit has been shown to regulate the ion flow. Herein, we demonstrated that the ion flow was terminated by the crosslinking between the plug region and the A subunit. These finding support the rotation hypothesis and explain the role of the plug region in terminating the rotation.

microbiology↗

bioRxiv2021

Site-directed crosslinking identifies the stator-rotor interaction surfaces in a hybrid bacterial flagellar motor

The bacterial flagellum is the motility organelle powered by a rotary motor. The rotor and stator elements of the motor are embedded in the cytoplasmic membrane. The stator units assemble around the rotor, and an ion flux (typically H+ or Na+) conducted through a channel of the stator induces conformational changes that generate rotor torque. Electrostatic interactions between the stator protein PomA in Vibrio (MotA in Escherichia coli) and the rotor protein FliG have been suggested by genetic analyses, but have not been demonstrated directly. Here, we used site-directed photo- and disulfide-crosslinking to provide direct evidence for the interaction. We introduced a UV-reactive amino acid, p-benzoyl-L-phenylalanine (pBPA), into the cytoplasmic region of PomA or the C-terminal region of FliG in intact cells. After UV irradiation, pBPA inserted at a number of positions formed a crosslink with FliG. PomA residue K89 gave the highest yield of crosslinks, suggesting that it is the PomA residue nearest to FliG. UV-induced crosslinking stopped motor rotation, and the isolated hook-basal body contained the crosslinked products. pBPA inserted to replace residues R281 or D288 in FliG formed crosslinks with the Escherichia coli stator protein, MotA. A cysteine residue introduced in place of PomA K89 formed disulfide crosslinks with cysteine inserted in place of FliG residues R281 and D288, and some other flanking positions. These results provide the first demonstration of direct physical interaction between specific residues in FliG and PomA/MotA.

microbiology↗

bioRxiv2021

Role of the N- and C-terminal regions of FliF, the MS ring component in Vibrio flagellar basal body

The MS ring is a part of the flagellar basal body and formed by 34 subunits of FliF, which consists of a large periplasmic region and two transmembrane segments connected to the N- and C-terminal regions facing the cytoplasm. A cytoplasmic protein, FlhF, which determines the position and number of the basal body, supports MS ring formation in the membrane. In this study, we constructed FliF deletion mutants that lack 30 or 50 residues at the N-terminus ({Delta}N30 and {Delta}N50), and 83 ({Delta}C83) or 110 residues ({Delta}C110) at the C-terminus. The N-terminal deletions were functional and conferred motility of Vibrio cells, whereas the C-terminal deletions were nonfunctional. The mutants were expressed in Escherichia coli to determine whether an MS ring could still be assembled. When co-expressing {Delta}N30FliF or {Delta}N50FliF with FlhF, fewer MS rings were observed than with the expression of wild-type FliF, in the MS ring fraction, suggesting that the N-terminus interacts with FlhF. MS ring formation is probably inefficient without an additional factor or FlhF. The deletion of the C-terminal cytoplasmic region did not affect the ability of FliF to form an MS ring because a similar number of MS rings were observed for {Delta}C83FliF as with wild-type FliF, although further deletion of the second transmembrane segment ({Delta}C110FliF) abolished it. These results suggest that the terminal regions of FliF have distinct roles; the N-terminal region for efficient MS ring formation and the C-terminal region for MS ring function. The second transmembrane segment is indispensable for MS ring assembly. ImportanceThe bacterial flagellum is a supramolecular architecture involved in cell motility. At the base of the flagella, a rotary motor that begins to construct an MS ring in the cytoplasmic membrane comprises 34 transmembrane proteins (FliF). Here, we investigated the roles of the N and C terminal regions of FliF, which are MS rings. Unexpectedly, the cytoplasmic regions of FliF are not indispensable for the formation of the MS ring, but the N-terminus appears to assist in ring formation through recruitment of FlhF, which is essential for flagellar formation. The C-terminus is essential for motor formation or function.

microbiology↗

bioRxiv2018

Cascaded Processing of Amplitude Modulation for Natural Sound Recognition

Temporal variation of sound envelope, or amplitude modulation (AM), is essential for auditory perception of natural sounds. Neural representation of stimulus AM is successively transformed while processed by a cascade of brain regions in the auditory system. Here we sought the functional significance of such cascaded transformation of AM representation. We modelled the function of the auditory system with a deep neural network (DNN) optimized for natural sound recognition. Neurophysiological analysis of the DNN revealed that AM representation similar to the auditory system emerged during the optimization. The better-recognizing DNNs exhibited larger similarity to the auditory system. The control experiments suggest that the cascading architecture, the data structure, and the optimization objective may be essential factors for the lower, middle and higher regions, respectively. The results were consistently observed across independent datasets. These results suggest the emergence of AM representation in the auditory system during optimization for natural sound recognition.

neuroscience↗

bioRxiv2017

Thalamocortical Projectional Divergence Leads to Complexity in Functional Organizations in Mouse Auditory Cortex

Frequency-related topological projections from the ventral division of the medial geniculate body (MGv) relay the tonotopic organization found in primary auditory cortex (A1). However, relaying circuits of the functional organization to higher-order, secondary auditory field (A2) have not been identified so far. Here, using tracing, we found that A2 receives dense topological projections from MGv in mice, and that tonotopy was established in A2 even when primary fields including A1 were removed. These indicate that thalamic inputs to A2 are sufficient for generating its tonotopy. Moreover, neuronal responses in the thalamocortical recipient layer of A2 showed wider bandwidth and greater heterogeneity of the best frequency distribution than those of A1, which was attributed to larger divergence of thalamocortical projections from MGv to A2 than those from MGv to A1. The current study identifies that the functional organization in the auditory cortex can be determined by the structure of thalamocortical input.\n\nSignificant StatementAlthough peripheral input patterns to the primary auditory cortex (A1) of the brain are well understood, how tonal information is relayed to higher-order regions such as the secondary auditory field (A2) remains unclear. This work revealed a new source of auditory information to A2; the tonal map in mouse A2 is primarily produced by orderly projections from the primary auditory thalamus. We also found that the complex behaviour and organization of neurons in A2 is generated by divergent projections from the primary thalamus that converge on neurons in A2. Our findings indicate that thalamocortical projections constitute a major factor that determines the regional properties and functional organization of mouse A2.

neuroscience↗