Effect of temperature on actin filament corkscrewing driven by nonprocessive myosin IC

Myosin family proteins are ATP-driven, actin filament-based motor proteins that generate force along actin filaments. In in vitro actin filament gliding assays, certain myosins generate rotation of gliding actin filaments around their long axes. In this study, we assessed the effects of temperature on the corkscrewing motion of actin filaments, including factors like gliding and rotational velocities and corkscrewing pitch. The corkscrewing motion was driven by a nonprocessive, full-length single-headed Drosophila myosin IC attached to an antibody adsorbed onto a cover glass. We performed an in vitro actin filament corkscrewing assay at temperatures ranging from 25 °C to 35 °C. We found that the gliding and rotational velocities and the pitch of corkscrewing actin filaments generated by myosin IC molecules increased with increasing temperature. Since the pitch is determined by dividing the gliding velocity by the rotational velocity, an increase in the pitch indicates that the gliding velocity increased faster than the rotational velocity with increasing temperature. These results suggest that temperature has distinct effects on the gliding and rotational forces produced by myosin IC, with implications for interpreting the temperature effect on torque-generation mechanisms driven by myosins on actin filaments at physiological temperatures.

Myosin-induced F-actin fragmentation facilitates contraction of actin networks

Mechanical forces play a crucial role in diverse physiological processes, such as cell migration, cytokinesis, and morphogenesis. The actin cytoskeleton generates a large fraction of the mechanical forces via molecular interactions between actin filaments (F-actins) and myosin motors. Recent studies have shown that the common tendency of actomyosin networks to contract into a smaller structure deeply involves F-actin buckling induced by motor activities, fragmentation of F-actins, and the force-dependent unbinding of cross-linkers that inter-connect F-actins. The fragmentation of F-actins was shown to originate from either buckling or tensile force from previous single-molecule experiments. While the role of buckling in network contraction has been studied extensively, to date, the role of tension-induced F-actin fragmentation in network contraction has not been investigated. In this study, we employed in vitro experiments and an agent-based computational model to illuminate when and how the tension-induced F-actin fragmentation facilitates network contraction. Our experiments demonstrated that F-actins can be fragmented due to tensile forces, immediately followed by catastrophic rupture and contraction of networks. Using the agent-based model, we showed that F-actin fragmentation by tension results in distinct rupture dynamics different from that observed in networks only with cross-linker unbinding. Moreover, we found that tension-induced F-actin fragmentation is particularly important for the contraction of networks with high connectivity. Results from our study shed light on an important regulator of the contraction of actomyosin networks which has been neglected. In addition, our results provide insights into the rupture mechanisms of polymeric network structures and bio-inspired materials.

Membrane-bound myosin IC drives the chiral rotation of the gliding actin filament around its longitudinal axis

Myosin IC, a single-headed member of the myosin I family, specifically interacts with anionic phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2) in the cell membrane via the pleckstrin homology domain located in the myosin IC tail. Myosin IC is widely expressed and physically links the cell membrane to the actin cytoskeleton; it plays various roles in membrane-associated physiological processes, including establishing cellular chirality, lipid transportation, and mechanosensing. In this study, we evaluated the motility of full-length myosin IC of Drosophila melanogaster via the three-dimensional tracking of quantum dots bound to actin filaments that glided over a membrane-bound myosin IC-coated surface. The results revealed that myosin IC drove a left-handed rotational motion in the gliding actin filament around its longitudinal axis, indicating that myosin IC generated a torque perpendicular to the gliding direction of the actin filament. The quantification of the rotational motion of actin filaments on fluid membranes containing different PI(4,5)P2 concentrations revealed that the rotational pitch was longer at lower PI(4,5)P2 concentrations. These results suggest that the torque generated by membrane-bound myosin IC molecules can be modulated based on the phospholipid composition of the cell membrane.

Fission yeast Dis1 is an unconventional TOG/XMAP215 that induces microtubule catastrophe to drive chromosome pulling

The shortening of microtubules attached to kinetochores is the driving force of chromosome movement during cell division. Specific kinesins are believed to shorten microtubules but are dispensable for viability in yeast, implying the existence of additional factors responsible for microtubule shortening. Here, we demonstrate that Dis1, a TOG/XMAP215 ortholog in fission yeast, promotes microtubule shortening to carry chromosomes. Although TOG/XMAP215 orthologs are generally accepted as microtubule polymerases, Dis1 promoted microtubule catastrophe in vitro and in vivo. Notably, microtubule catastrophe was promoted when the tip was attached to kinetochores, as they steadily anchored Dis1 at the kinetochore-microtubule interface. Engineered Dis1 oligomers artificially tethered at a chromosome arm region induced the shortening of microtubules in contact, frequently pulling the chromosome arm towards spindle poles. This effect was not brought by oligomerised Alp14. Thus, unlike Alp14 and other TOG/XMAP215 orthologs, Dis1 plays an unconventional role in promoting microtubule catastrophe, thereby driving chromosome movement.

Three-dimensional tracking of the ciliate Tetrahymena reveals the mechanism of ciliary stroke-driven helical swimming

Helical swimming in free-space is a common behavior among microorganisms, such as ciliates that are covered with thousands hair-like motile cilia, and is thought to be essential for cells to orient directly to an external stimulus. However, a direct quantification of their three-dimensional (3D) helical trajectories has not been reported, in part due to difficulty in tracking 3D swimming behavior of ciliates, especially Tetrahymena with a small, transparent cell body. Here, we conducted 3D tracking of fluorescent microbeads within a cell to directly visualize the helical swimming exhibited by Tetrahymena. Our technique showed that Tetrahymena swims along a right-handed helical path with right-handed rolling of its cell body. Using the Tetrahymena cell permeabilized with detergent treatment, we also observed that influx of Ca²⁺ into cilia changed the 3D-trajectory patterns of Tetrahymena swimming, indicating that the beating pattern of cilia is the determining factor in its swimming behavior.

Identifying patients with atrial fibrillation during sinus rhythm on ECG: confirming the utility of artificial intelligence algorithm in a small-scale cohort without structural heart diseases

Background

Detection of atrial fibrillation (AF) out of electrocardiograph (ECG) on sinus rhythm (SR) using artificial intelligence (AI) algorithm has been widely studied within recent couple of years. Generally, it is believed that a huge number of ECGs are necessary for developing an AI-enabled ECG to be adequate to correspond to a lot of minor variations of ECGs. For example, structural heart diseases have typical ECG characteristics, but they could be a noise for the purpose of detecting the small signs of electrocardiographic signature of AF. We hypothesized that when patients with structural heart diseases are excluded, AI-enabled ECG for identifying patients with AF can be developed with a small number of ECGs.

Methods

We developed an AI-enabled ECG using a convolutional neural network to detect the electrocardiographic signature of AF present during normal sinus rhythm (NSR) using a digital, standard 10-second, 12-lead ECGs. We included all patients who newly visited the Cardiovascular Institute with at least one NSR ECG between Feb 1, 2010, and March 31, 2018. We classified patients with at least one ECG with a rhythm of AF as positive for AF (AF label) and others as negative for AF (SR label). We allocated ECGs to the training, internal validation, and testing datasets in a 7:1:2 ratio. We calculated the area under the curve (AUC) of the receiver operating characteristic curve for the internal validation dataset to select a probability threshold, which we applied to the testing dataset. We evaluated model performance on the testing dataset by calculating the AUC and the sensitivity, specificity, F1 score, and accuracy with two-sided 95% confidence intervals (CIs).

Results

We totally included 19170 patients with 12-lead ECG. After excluding patients with structural heart diseases, 12825 patients with NSR ECGs at the initial visit were identified (1262 were clinically diagnosed as AF anytime during the time course and 11563 were never diagnosed as AF). Of 11563 non-AF patients, 1818 patients who were followed over 1095 days were selected for the analysis with the SR label, to secure the robustness for maintaining SR. Of 1262 AF patients, 251 patients were selected for the analysis with the AF label, of whom a NSR ECG within 31 days before or after the index AF ECG (the first AF ECG during the time course) could be obtained. In the patients with AF label, the NSR ECG of which the date was the nearest to the index AF ECG was selected for the analysis. The AI-enabled ECG showed an AUC of 0.88 (0.84–0.92) with sensitivity 81% (72–88), specificity 80% (77–83), F1 score 50% (43–57), and overall accuracy 80% (78–83).

Conclusion

An AI-enabled ECG acquired during NSR allowed identification of patients with AF in a small population without structural heart diseases.

Funding Acknowledgement

Type of funding sources: None.

Characterization of the motility of monomeric kinesin-5/Cin8

Cin8, the Saccharomyces cerevisiae kinesin-5, has an essential role in mitosis. In in vitro motility assays, tetrameric and dimeric Cin8 constructs showed bidirectional motility in response to ionic strength or Cin8 motor density. However, whether property-switching directionality is present in a monomeric form of Cin8 is unknown. Here we engineered monomeric Cin8 constructs with and without the Cin8-specific ∼99 residues in the loop 8 domain and examined the directionality of these constructs using an in vitro polarity-marked microtubule gliding assay within the range of the motor density or ionic strength. We found that both monomeric constructs showed only plus end-directed activity over the ranges measured, which suggested that minus end-directed motility driven by Cin8 is necessary for at least dimeric forms. Using an in vitro microtubule corkscrewing assay, we also found that monomeric Cin8 corkscrewed microtubules around their longitudinal axes with a constant left-handed pitch. Overall, our results imply that plus-end-directed and left-handed motor activity comprise the intrinsic properties of the Cin8 motor domain as with other monomeric N-kinesins.

A Study Validating the Estimation of Anterior Chamber Depth and Iridocorneal Angle with Portable and Non-Portable Slit-Lamp Microscopy

This study assessed the anterior chamber depth (ACD) and iridocorneal angle using a portable smart eye camera (SEC) compared to the conventional slit-lamp microscope and anterior-segment optical coherence tomography (AS-OCT). This retrospective case-control study included 170 eyes from 85 Japanese patients. The correlation between the ACD evaluations conducted with the SEC and conventional slit-lamp was high (r = 0.814). The correlation between the Van-Herick Plus grade obtained using two devices was also high (r = 0.919). A high kappa value was observed for the Van-Herick Plus grading (Kappa = 0.757). A moderate correlation was observed between the ACD measured using AS-OCT and the slit-lamp image acquired with the conventional slit-lamp microscope and SEC (r = 0.609 and 0.641). A strong correlation was observed between the trabecular-iris angle (TIA) measured using AS-OCT and Van-Herick Plus grade obtained with the conventional slit-lamp microscope and SEC (r = 0.702 and 0.764). Strong correlations of ACD evaluation and high kappa value of the Van-Herick Plus grading indicated the adequate subjective assessment function of the SEC. Moderate correlations between the ACD objective measurement and evaluation and strong correlation between the TIA and Van-Herick Plus grade suggested the good objective assessment function of the SEC. The SEC demonstrated adequate performance for ACD evaluation and angle estimation.

CYK4 relaxes the bias in the off-axis motion by MKLP1 kinesin-6

Centralspindlin, a complex of the MKLP1 kinesin-6 and CYK4 GAP subunits, plays key roles in metazoan cytokinesis. CYK4-binding to the long neck region of MKLP1 restricts the configuration of the two MKLP1 motor domains in the centralspindlin. However, it is unclear how the CYK4-binding modulates the interaction of MKLP1 with a microtubule. Here, we performed three-dimensional nanometry of a microbead coated with multiple MKLP1 molecules on a freely suspended microtubule. We found that beads driven by dimeric MKLP1 exhibited persistently left-handed helical trajectories around the microtubule axis, indicating torque generation. By contrast, centralspindlin, like monomeric MKLP1, showed similarly left-handed but less persistent helical movement with occasional rightward movements. Analysis of the fluctuating helical movement indicated that the MKLP1 stochastically makes off-axis motions biased towards the protofilament on the left. CYK4-binding to the neck domains in MKLP1 enables more flexible off-axis motion of centralspindlin, which would help to avoid obstacles along crowded spindle microtubules.

Analysing the 3D movement of MKLP1 motors, Maruyama et al. find that dimeric C. elegans MKLP1 drives a left-handed helical motion around the microtubule with minimum protofilament switching to the right side whereas less persistent motions are driven by monomers or by heterotetramers with CYK4. These findings suggest how obstacles along crowded spindle microtubules may be avoided by CYK4 binding to MKLP1.

Prediction of atrial fibrillation by 12-lead electrocardiogram parameters in patients without structural heart disease

Background

Recently, the analysis of electrocardiogram (ECG) waveform by artificial intelligence has been reported to pick out those who have atrial fibrillation (AF) or have a high potential of developing AF, which, however, cannot explain the mechanisms or algorisms for the prediction from its nature.

Purpose

The purpose of this study is to conduct a comprehensive analysis to investigate the difference of weighting in predicting capability for AF among hundreds of automatically-measured ECG parameters using a single ECG at sinus rhythm.

Methods and results

Out of Shinken Database 2010–2017 (n=19170), 12825 patients were extracted, where those with ECG showing AF rhythm at the initial visit (including all persistent/permanent AF and a part of paroxysmal AF) and those with structural heart diseases were excluded. Out of 639 automatically-measured ECG parameters in MUSE data management system (GE Healthcare, USA), 438 were used. [Analysis 1] A predicting model for paroxysmal AF were determined by logistic regression analysis (Total, n=12825; paroxysmal AF, n=1138), showing a high predictive capability (AUC = 0.780, p<0.001). In this model, the relative contribution of ECG parameters (by coefficient of determination) according to the time phase were P:72.4%, QRS:32.7%, and ST-T:13.7%, respectively (Figure A). [Analysis 2] Excluding AF at baseline, a predicting model for new-developed AF were determined by Cox regression analysis (Total, n=11687; new-developed AF, n=87), showing a high predictive capability (AUC = 0.887, p<0.001). In this model, the relative contribution of parameters (by log likelihood) according to the time phase were P:40.8%, QRS:42.5%, and ST-T:24.9%, respectively (Figure B).

Conclusions

We determined ECG parameters that potentially contribute to picking up existing AF or predicting future development of AF, where the measurement of P wave strongly contributed in the former whereas all time phases were similarly important in the latter.

Weighting of parameters to predict AF

Funding Acknowledgement

Type of funding source: Private hospital(s). Main funding source(s): Self funding of the institute

Heart rate recovery after exercise as a prognostic predictor in patients with atrial fibrillation

Background

A delayed heart rate recovery (HRR) after exercise is related to mortality in sinus rhythm. This study aimed to investigate this concept can be applied to patients with atrial fibrillation (AF).

Methods

We analyzed 483 patients with AF (mean 65 years, male 74%). HRR integral was calculated by integrating the difference in HR in every 3 second between the end of exercise and the specified time after the exercise (30, 60, 120 and 180 seconds). After evaluating the prognostic power of each HRR integral, we selected HRR integral of 180 seconds (180HRR-integral).

Results

We divided the patients into two groups using median value of 180HRR-integral. All-cause mortality, the incidence of cardiovascular events and heart failure events were higher in the poor 180HRR-integral. After adjustment for covariates, the impact of the high 180HRR-integral for all-cause mortality was 3.15 (p=0.057), 1.77 for cardiovascular events (p=0.067) and 1.28 for heart failure events (p=0.519).

Conclusion

Poor HRR was associated with worse prognosis in patients with AF.

Funding Acknowledgement

Type of funding source: None

153 Multiparametric assessment of diastolic function in heart failure

Background

The assessment of diastolic function is still challenging in the setting of heart failure (HF). We tested the hypothesis that applying a machine learning algorithm would detect heterogeneity in diastolic function and improve risk stratification in HF population.

Methods

This study included consecutive 279 patients with clinically stable HF referred for echocardiographic assessment, for whom diastolic function variables were measured according to the current guidelines. Cluster analysis, an unsupervised machine learning algorithm, was undertaken on these variables to form homogeneous groups of patients with similar profiles of the variables. Sequential Cox models paralleling the clinical sequence of HF assessment were used to elucidate the benefit of cluster-based classification over guidelines-based classification. The primary endpoint was a hospitalization for worsening HF.

Results

Cluster analysis identified 3 clusters with distinct properties of diastolic function that shared similarities with guidelines-based classification. The clusters were associated with brain natriuretic peptide level (p < 0.001, figure A). During follow-up period of 2.6 ± 2.0 years, 62 patients (22%) experienced the primary endpoint. Cluster-based classification exhibited a significant prognostic value (c2 = 20.3, p < 0.001, figure B), independent from and incremental to an established clinical risk score for HF (MAGGIC score) and left ventricular end-diastolic volume (hazard ratio = 1.677, p = 0.017, model c2: from 47.5 to 54.1, p = 0.015, figure D). Although guideline-based classification showed a significant prognostic value (c2 = 13.1, p = 0.001, figure C), it did not significantly improve overall prognostication from the baseline (model c2: from 47.5 to 49.9, p = 0.199, figure D).

Conclusion

Machine learning techniques help grading diastolic function and stratifying the risk for decompensation in HF.

Abstract 153 Figure.

P289 Aortic valve resistance risk-stratifies low-gradient aortic stenosis

Background

Grading the severity of aortic stenosis (AS) is challenging, since there is a discrepancy between aortic valve area (AVA) and mean pressure gradient (mPG). Arotic valve resistance (RES) has been proposed as a usuful descriptor of AS severity, but it is not commonly used for clinical decision-making, because its robust validation of clinical-outcome efficacy is lacking. This study aimed to investigate whether RES holds an incremental value for risk-stratifying AS.

Methods

This study recuited 565 AS patients (AVA < 1.5cm²) referred to echocardiography for valve assessment. The patients were divided into three different groups, according to the guidelines: high-gradient AS (HG-AS, mPG≥40mmHg, n = 157), low-gradient AS (LG-AS, mPG < 40mmHg + AVA ≤ 1.0cm², n = 155) and moderate AS (Mod-AS, mPG < 40mmHg + AVA > 1.0cm², n = 253). RES was calculated from Doppler measurement of mPG and stoke volume. The diagnositic cutoff point for RES was determined at 190 dynes × s×cm-5 by substituting AVA = 1.0cm² and mPG = 40mmHg into the definition formula of RES and Gorlin formula. The patients were followed up for 2 years. The endpoint was a composite of cardiac death, hospitalization for heart failure and aortic valve replacement necessitated by the development of AS-related symptoms.

Result

Kaplan-Meier analyses showed that LG-AS exhibited an intermediate outcome between HG-AS and Mod-AS (event-free survival at 2 years = 20.9% for HG-AS, 59.7% for LG-AS, 89.9% for Mod-AS, p < 0.001, figure A). When LG-AS was stratified by RES, the survival curves showed a significant separation (event-free survival at 2 years = 35.3% for high RES, 70.7% for low RES, p < 0.001, figure B). This trend persisted even when analysed separately for norml (stroke volume index > 35ml/m²) and low (stroke volume index ≤ 35ml/m²) flow state ((normal flow) event-free survival at 2 years = 38.7% for high RES, 70.4% for low RES, p = 0.023, figure C; (low flow) event-free survival at 2 years = 26.7% for high RES, 74.6% for low RES, p < 0.001, figure D).

Conclusion

This study confirmed the clinical efficacy of RES for risk-stratifying LG-AS patients.

Abstract P289 Figure.

Effect of attention bias modification on event-related potentials in patients with irritable bowel syndrome: A preliminary brain function and psycho-behavioral study

BACKGROUND

Attention bias modification normalizes electroencephalographic abnormalities in alpha and beta power percentages related to attention in patients with irritable bowel syndrome (IBS). Yet, it is unknown whether ABM contributes to the normalization of event-related potentials (ERP) in these patients. We hypothesized that ERP related to attention deficit would be normalized after ABM implementation in individuals with IBS.

METHODS

Thirteen patients with IBS and 10 control subjects completed a 2-month intervention that included five ABM sessions. Each session included 128 trials, resulting in a total of 640 trials during the study period. Event-related potentials were measured at the first and fifth sessions. As per the international 10-20 system for electroencephalographic electrode placement, right parietal P4 was evaluated to measure the attention component of facial expression processing.

KEY RESULTS

A group comparison of P100 latency at P4 revealed that latencies were significantly different between groups in session 1 (IBS vs control, 108 ± 8 vs 97 ± 14; t = -2.51, P = .0203). This difference was absent in session 5 (94 ± 11 vs 93 ± 11, respectively; t = -0.397, P = .6954, r = .09), indicating an effect of ABM in the IBS group.

CONCLUSIONS AND INFERENCES

Attention bias modification may have clinical utility for normalizing brain function and specifically attentional abnormalities in patients with IBS.

Circular orientation fluorescence emitter imaging (COFEI) of rotational motion of motor proteins

Single-molecule fluorescence polarization technique has been utilized to detect structural changes in biomolecules and intermolecular interactions. Here we developed a single-molecule fluorescence polarization measurement system, named circular orientation fluorescence emitter imaging (COFEI), in which a ring pattern of an acquired fluorescent image (COFEI image) represents an orientation of a polarization and a polarization factor. Rotation and pattern change of the COFEI image allow us to find changes in the polarization by eye and further values of the parameters of a polarization are determined by simple image analysis with high accuracy. We validated its potential applications of COFEI by three assays: 1) Detection of stepwise rotation of F₁-ATPase via single quantum nanorod attached to the rotary shaft γ; 2) Visualization of binding of fluorescent ATP analog to the catalytic subunit in F₁-ATPase; and 3) Association and dissociation of one head of dimeric kinesin-1 on the microtubule during its processive movement through single bifunctional fluorescent probes attached to the head. These results indicate that the COFEI provides us the advantages of the user-friendly measurement system and persuasive data presentations.

Dissection of the angle of single fluorophore attached to the nucleotide in corkscrewing microtubules

Direct dissection of the angles of single fluorophores under an optical microscope has been a challenging approach to study the dynamics of proteins in an aqueous solution. For angle quantifications of single substrates, however, there was only one report (Nishizaka et al., 2014) because of difficulties of construction of experimental systems with active proteins working at the single-molecule level. We here show precise estimation of orientation of single fluorescent nucleotides bound to single tubulins that comprise microtubule. When single-headed kinesins immobilized on a glass surface drive the sliding of microtubules, microtubules show corkscrewing with regular pitches (Yajima et al., 2005 & 2008). We found, by using a three-dimensional tracking microscope, that S8A mutant kinesin also showed precise corkscrewing with a 330-nm pitch, which is 13% longer than that of the wild type. The assay with the mutant was combined with a defocused imaging technique to visualize the rotational behavior of fluorescent nucleotide bound to corkscrewing microtubule. Notably, the defocused pattern of single TAMRA-GTP periodically changed, precisely correlating to its precession movement. The time course of the change in the fluorophore angle projected to the xy-plane enabled to estimate both the fluorophore orientation against microtubule axis and the precision of angle-determination of analyses system. The orientation showed main distribution with peaks at∼40°, 50° and 60°. To identify their molecular conformations, the rigorous docking simulations were performed using an atomic-level structure modeled by fitting x-ray crystal structures to the cryo-electron microscopy map. Among isomers, 2'-O-EDA-GDP labeled with 5- or 6-TAMRA were mainly specified as possible candidates as a substrate, which suggested the hydrolysis of TAMRA-GTP by tubulins.

Augmin shapes the anaphase spindle for efficient cytokinetic furrow ingression and abscission

During anaphase, distinct populations of microtubules (MTs) form by either centrosome-dependent or augmin-dependent nucleation. It remains largely unknown whether these different MT populations contribute distinct functions to cytokinesis. Here we show that augmin-dependent MTs are required for the progression of both furrow ingression and abscission. Augmin depletion reduced the accumulation of anillin, a contractile ring regulator at the cell equator, yet centrosomal MTs were sufficient to mediate RhoA activation at the furrow. This defect in contractile ring organization, combined with incomplete spindle pole separation during anaphase, led to impaired furrow ingression. During the late stages of cytokinesis, astral MTs formed bundles in the intercellular bridge, but these failed to assemble a focused midbody structure and did not establish tight linkage to the plasma membrane, resulting in furrow regression. Thus augmin-dependent acentrosomal MTs and centrosomal MTs contribute to nonredundant targeting mechanisms of different cytokinesis factors, which are required for the formation of a functional contractile ring and midbody.

Torque generation by axonemal outer-arm dynein

Outer-arm dynein is the main engine providing the motive force in cilia. Using three-dimensional tracking microscopy, we found that contrary to previous reports Tetrahymena ciliary three-headed outer-arm dynein (αβγ) as well as proteolytically generated two-headed (βγ) and one-headed (α) subparticles showed clockwise rotation of each sliding microtubule around its longitudinal axis in microtubule corkscrewing assays. By measuring the rotational pitch as a function of ATP concentration, we also found that the microtubule corkscrewing pitch is independent of ATP concentration, except at low ATP concentrations where the pitch generated by both three-headed αβγ and one-headed α exhibited significantly longer pitch. In contrast, the pitch driven by two-headed βγ did not display this sensitivity. In the assays on lawns containing mixtures of α and βγ at various ratios, the corkscrewing pitch increased dramatically in a nonlinear fashion as the ratio of α in the mixture increased. Even small proportions of α-subparticle could significantly increase the corkscrewing pitch of the mixture. Our data show that torque generation does not require the three-headed outer-arm dynein (αβγ) but is an intrinsic property of the subparticles of axonemal dyneins and also suggest that each subparticle may have distinct mechanical properties.

Axonemal dynein light chain-1 locates at the microtubule-binding domain of the γ heavy chain

Dynein light chain 1 (LC1) of the outer arm dynein (OAD) complex associates with the microtubule-binding domain (MTBD) of γ heavy chain inside the complex. LC1 is considered to regulate the OAD activity and ciliary/flagellar motion by modulating γ MTBD's affinity to the B-tubule of the doublet microtubule in the axoneme.

The outer arm dynein (OAD) complex is the main propulsive force generator for ciliary/flagellar beating. In Chlamydomonas and Tetrahymena, the OAD complex comprises three heavy chains (α, β, and γ HCs) and >10 smaller subunits. Dynein light chain-1 (LC1) is an essential component of OAD. It is known to associate with the Chlamydomonas γ head domain, but its precise localization within the γ head and regulatory mechanism of the OAD complex remain unclear. Here Ni-NTA-nanogold labeling electron microscopy localized LC1 to the stalk tip of the γ head. Single-particle analysis detected an additional structure, most likely corresponding to LC1, near the microtubule-binding domain (MTBD), located at the stalk tip. Pull-down assays confirmed that LC1 bound specifically to the γ MTBD region. Together with observations that LC1 decreased the affinity of the γ MTBD for microtubules, we present a new model in which LC1 regulates OAD activity by modulating γ MTBD's affinity for the doublet microtubule.

Nanoscale localization sampling based on nanoantenna arrays for super-resolution imaging of fluorescent monomers on sliding microtubules

Sub-diffraction-limited imaging of fluorescent monomers on sliding microtubules in vitro by nanoscale localization sampling (NLS) is reported. NLS is based on periodic nanohole antenna arrays that create locally amplified electromagnetic hot spots through surface plasmon localization. The localized near-field hot spot temporally samples microtubular movement for enhanced spatial resolution. A fourfold improvement in spatial resolution compared to conventional wide-field microscopy is demonstrated. The resolution enhancement is achieved by imaging rhodamine-labeled microtubules that are sampled by the hot spots to provide sub-diffraction-limited images at 76 nm resolution in the direction of movement and 135 nm orthogonally. The intensity distribution produced by the NLS is measured to be broader than that of conventional imaging, which is consistent with the improvement of imaging resolution. Correlation studies between neighboring nanoantennas are also performed. This confirms the possibility of measuring microtubular transport dynamics. NLS can be useful for moving objects that have a high labeling density or for performing fluctuation spectroscopy in small volumes, and may allow "super-resolution on demand" by customizing nanoantenna structures for specific resolution needs.

Single-particle tracking of quantum dot-conjugated prion proteins inside yeast cells

Yeast is a model eukaryote with a variety of biological resources. Here we developed a method to track a quantum dot (QD)-conjugated protein in the budding yeast Saccharomyces cerevisiae. We chemically conjugated QDs with the yeast prion Sup35, incorporated them into yeast spheroplasts, and tracked the motions by conventional two-dimensional or three-dimensional tracking microscopy. The method paves the way toward the individual tracking of proteins of interest inside living yeast cells.

A torque component in the kinesin-1 power stroke

Kinesin-1 is a twin-headed molecular motor that moves along microtubules in 8-nm steps, using a walking action in which the two heads interact alternately with the microtubule. Constructs with only one head can also produce impulses of force and motion, indicating that the walking action is an amplification strategy that leverages an underlying force-generating event. Recent work suggests that directional force is produced either by directionally biased selection of microtubule binding sites or by a conformational change subsequent to the binding event. We report here that surface-attached rat kinesin-1 monomers drive counterclockwise rotation of sliding microtubules around their axes, and that by manipulating the assay geometry, we could reduce or block the torsional motion with negligible effects on the axial motion. We can account for this behavior on the simple assumption that kinesin heads tend to bind to the closest available tubulin heterodimer in the lattice, but only in the case where an additional biasing process is present that shifts the start position for diffusion-to-capture toward the microtubule plus end by approximately 1 nm.

The human chromokinesin Kid is a plus end-directed microtubule-based motor

Kid is a kinesin-like DNA-binding protein known to be involved in chromosome movement during mitosis, although its actual motor function has not been demonstrated. Here, we describe the initial characterization of Kid as a microtubule-based motor using optical trapping microscopy. A bacterially expressed fusion protein consisting of a truncated Kid fragment (amino acids 1-388 or 1-439) is indeed an active microtubule motor with an average speed of approximately 160 nm/s, and the polarity of movement is plus end directed. We could not detect processive movement of either monomeric Kid or dimerizing chimeric Kid; however, low levels of processivity (a few steps) cannot be detected with our method. These results are consistent with Kid having a role in chromosome congression in vivo, where it would be responsible for the polar ejection forces acting on the chromosome arms.

A novel action of terpendole E on the motor activity of mitotic Kinesin Eg5

To reveal the mechanism of mitosis, the development of M phase-specific inhibitors is an important strategy. We have been screening microbial products to find specific M phase inhibitors that do not directly target tubulins, and rediscovered terpendole E (TerE) as a novel Eg5 inhibitor. TerE did not affect microtubule integrity in interphase, but induced formation of a monoastral spindle in M phase. TerE inhibited both motor and microtubule-stimulated ATPase activities of human Eg5, but did not affect conventional kinesin from either Drosophila or bovine brain. Although terpendoles have been reported as inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT), the Eg5 inhibitory activity of TerE was independent of ACAT inhibition. Taken together, we demonstrate that TerE is a novel Eg5 inhibitor isolated from a fungal strain.

Kinesin-microtubule binding depends on both nucleotide state and loading direction

Kinesin is a motor protein that transports organelles along a microtubule toward its plus end by using the energy of ATP hydrolysis. To clarify the nucleotide-dependent binding mode, we measured the unbinding force for one-headed kinesin heterodimers in addition to conventional two-headed kinesin homodimers under several nucleotide states. We found that both a weak and a strong binding state exist in each head of kinesin corresponding to a small and a large unbinding force, respectively; that is, weak for the ADP state and strong for the nucleotide-free and adenosine 5'-[beta,gamma-imido]triphosphate states. Model analysis showed that (i) the two binding modes in each head could be explained by a difference in the binding energy and (ii) the directional instability of binding, i.e., dependence of unbinding force on loading direction, could be explained by a difference in the characteristic distance for the kinesin-microtubule interaction during plus- and minus-end-directed loading. Both these factors must play an important role in the molecular mechanism of kinesin motility.

Direct long-term observation of kinesin processivity at low load

The hand-over-hand stepping mechanism of kinesin at low loads is inadequately understood because the number of molecular steps taken per encounter with the microtubule is difficult to measure: optical traps do not register steps at zero load, while evanescent wave microscopy of single molecules of GFP-kinesin suffers from premature photobleaching. Obtaining low-load data is important because it can efficiently distinguish between alternative proposed mechanisms for molecular walking. We report a novel experiment that records the missing data. We fused kinesin to gelsolin, creating a construct that severs and caps rhodamine-phalloidin actin filaments, setting exactly one kinesin molecule on one end of each fluorescent actin filament. Single kinesin molecules labeled in this way can be tracked easily and definitively using a standard epifluorescence microscope. We use the new system to show that, contrary to a recent report, kinesin run length at low load is independent of ATP concentration in the muM to mM range of ATP concentration. Adding competitor ADP in the presence of saturating ATP decreases both velocity and run length. Based on these data, we propose a simplified model for the mechanism of processive stepping.

Intracoronary electrocardiogram for early detection of myocardial viability during coronary angioplasty in acute myocardial infarction

PURPOSE

The clinical value of the intracoronary electrocardiogram (ECG) for detecting myocardial viability in acute myocardial infarction was evaluated by thallium-201 scintigraphy and left ventriculogram at the chronic stage.

METHODS

Intracoronary ECGs, recorded from the tip of a guidewire during emergency coronary angioplasty, were obtained in 65 patients with reperfused anterior myocardial infarction. Further ST segment elevation of greater than 0.2 mV detected during the balloon inflation was taken as significant. The left ventricular segmental shortening was measured from left ventriculograms recorded at acute and chronic stages. The infarct area was defined as viable when a thallium uptake of more than 50% was detected on thallium-201 myocardial scintigraphy at the chronic stage.

RESULTS

During emergency coronary angioplasty, significant ST segment elevation was noted in 45 patients (Group A); however, the ST segment was not significantly elevated in the other 20 patients (Group B). The infarct area of 42 patients in Group A and three patients in Group B was viable on scintigraphy. Improvement left ventricular wall motion of the infarct area was observed in 39 of the 42 patients in Group A and the three patients in Group B. Therefore, intracoronary ECG can predict reversible dysfunction with excellent sensitivity (92.9%) and specificity (73.9%).

CONCLUSIONS

The myocardium within an infarct area can be regarded as viable when a further ST segment elevation occurs on intracoronary ECG during emergency coronary angioplasty. It is useful, therefore, to monitor the intracoronary ECG during coronary angioplasty balloon inflation to assess the myocardial viability of the infarct area.

Saliva level of free 3-methoxy-4-hydroxyphenylglycol (MHPG) as a biological index of anxiety disorders

To access the saliva level of free 3-methoxy-4-hydroxyphenylglycol (MHPG) as a biological index of anxiety disorders, gender- or age-dependent changes in saliva MHPG level in patients with anxiety disorders were investigated. Saliva MHPG levels in 196 normal volunteers (59 male, 137 female) and 42 outpatients with anxiety disorders (20 male, 22 female) at the initial consultation to the hospital were measured by gas chromatography-mass spectrometry. Saliva MHPG levels in patients were higher than those in normal subjects. The increase in saliva MHPG levels in male patients was greater than that in female patients. Age-associated increase in the saliva MHPG level was greater in patients than in normal subjects. Especially, a significant interaction of age vs. patient effect was found in female subjects (P=0.0005), but not in male subjects (P=0. 174). These data indicate that the measurement of saliva MHPG would be valuable for detecting pathological anxiety in male patients regardless of age and in older female patients, but not in younger female patients.

[Evaluation of coronary flow velocity and coronary flow reserve before and after coronary angioplasty using transthoracic Doppler echocardiography and Doppler guide wire]

Evaluation of left anterior descending coronary (LAD) blood flow before and after coronary angioplasty was carried out non-invasively by ultrasonic Doppler echocardiography with a newly developed digital, high-frequency, high-resolution transthoracic ultrasonic Doppler flowmeter and a 7.5 MHz probe. The results were compared with those obtained using an intracoronary Doppler guide wire. Sixteen patients, 12 males and 4 females (mean age 57 +/- 14 years) with old myocardial infarction (8 patients) and angina pectoris (8 patients) were studied. Coronary flow reserve was compared following intravenous administration of adenosine triphosphate in 12 patients. The LAD blood flow was detected in 15 of 16 patients. There was a significant increase in the diastolic peak velocity from 22.2 +/- 10.6 to 29.4 +/- 14.6 cm/sec (mean +/- SD) and the coronary flow reserve from 1.8 +/- 0.3 to 2.8 +/- 0.6 (mean +/- SD). There was a good correlation between the data obtained using transthoracic flow measurement and intracoronary flow measurement (r = 0.61, p < 0.05). LAD blood flow can be easily detected parasternally using a digital, high frequency, high-resolution ultrasonic Doppler flowmeter. This method may be applicable for judging the efficacy of coronary angioplasty by measuring coronary flow reserve and for observing the clinical course of the patient non-invasively.

[Saliva level of free-3-methoxy-4-hydroxyphenylglycol in patients with anxiety disorders]

The saliva level of free 3-methoxy-4-hydroxyphenylglycol (MHPG) in 16 outpatients with anxiety disorders was determined by gas chromatography-mass spectrometry. The anxiety level of the patients was scored by the Hamilton Anxiety Scale (HAS) before and after a one-week drug treatment with alprazolam. The saliva level of free-MHPG at the subjects' first visit to the hospital was significantly higher than that of the control subjects and was reduced by the one-week alprazolam treatment. The post-treatment level of MHPG in patients who showed good response to the treatment was significantly less than the pretreatment level, but there was no significant difference between pre- and post-treatment levels of MHPG in poor responders. There was no correlation between the MHPG level and the HAS score at the first hospital visit. The MHPG levels after the treatment correlated with the HAS scores. The reduction of the anxiety level as scored by the HAS correlated with the reduction of the MHPG level. These results indicate that the free saliva MHPG level may be a useful indicator for assessing not only the level of anxiety but also the response to drug treatment for anxiety in these patients.

Clinical utility of negative contrast intravascular ultrasound to evaluate plaque morphology before and after coronary interventions

Although intravascular ultrasound (IVUS) is used for evaluation of plaque volume and lumen size as well as detection of vessel wall structures after catheter-based interventions, differentiation between the lumen and plaque structures can be difficult. This study attempted to evaluate the efficacy of negative contrast IVUS imaging for assessment of vessel wall morphology after coronary interventions. IVUS studies were performed in 67 lesions in 66 patients before and after coronary interventions. After the baseline ultrasound imaging run, warm 5% glucose solution was injected manually through the guiding catheter into the coronary artery to washout blood from the lumen to avoid speckled reflections from red blood cells (negative contrast). Quantitative measurements were obtained and plaque morphology was assessed for the presence and extent of medial dissections and intimal flaps. There was no difference in each quantitative parameter between baseline images and negative contrast images. The vessel wall boundary was clearly delineated from the lumen, which was defined as effective negative contrast in 51 of 67 lesions (76%). The baseline images revealed plaque dissection in 9 lesions (18%) and an intimal flap in 13 lesions (25%). In addition, 4 dissections (8%) and 16 intimal flaps (31%) were visualized during the infusion of negative contrast. Additional treatment was performed in 4 lesions (8%) based on the images with negative contrast. Negative contrast IVUS was more sensitive in demonstrating a plaque fracture than were baseline images. This method is useful for enhancing the diagnostic capability of IVUS imaging and may influence the decision-making process during interventional procedures.

Saliva level of free 3-methoxy-4-hydroxyphenylglycol in psychiatric outpatients with anxiety

As a measurement of the level of anxiety in psychiatric outpatients with anxiety, we determined the saliva level of free 3-methoxy-4-hydroxyphenyleglycol (MHPG) using gas chromatography- mass spectrometry and scored the levels of anxiety with the Hamilton Anxiety Scale (HAS) in patients, before and after drug treatment with alprazolam for 1 week. The saliva level of free-MHPG at first visit to hospital was significantly higher than that of control individuals and disease control individuals and was reduced by alprazolam treatment for 1 week. There was no correlation between MHPG level and the HAS score at the first hospital visit. The MHPG levels after treatment correlated with the HAS scores. The reduction of the anxiety level as scored by the HAS correlated with the reduction of MHPG level. These results indicate that the free saliva MHPG level may be a useful indicator for assessing not only the level of anxiety, but also the response to drug treatment for anxiety in these patients.

Assessment of plaque rupture by intravascular ultrasound

To investigate the mechanism of plaque rupture, we carried out morphologic and quantitative assessments of ruptured plaque with a 30-MHz intravascular ultrasound catheter before coronary intervention. Plaque rupture, defined as an echolucent intraplaque area communicating with arterial lumen, was noted in all of 22 patients with coronary artery disease examined in the study. The plaque was eccentric in 16 patients (73%) and in 10 of these 16 patients there was a tear at the margin of the plaque (63%). Calcification was noted in only 6 patients (22%). Plaque area ranged from 8.7 to 44.1 mm2. The ruptured area ranged widely, from 1.0 to 14.0 mm2, and the percent ruptured area also ranged widely, from 3.9% to 50.9%. Fibrous cap was recognized in 20 patients. The thickness of the fibrous cap ranged from 0.1 to 0.6 mm (mean, 0.36 mm) and thinning of the fibrous cap was noted in 16 patients (80%). From these results, we conclude that intravascular ultrasound can provide detailed observations of plaque rupture consistent with pathologic studies. Accordingly, it is a suitable method for evaluation of plaque rupture in vivo. Plaque weakness, due to the presence of atheromatous core, thin fibrous cap, and no calcification, seems to be the major determinant of plaque rupture. In addition, the great variation in cap thickness and ruptured area suggests the role of other triggers, such as mechanical and hemodynamic stress, in plaque rupture.

Plaque rupture as a cause of apparent coronary aneurysm formation following directional coronary atherectomy

Late coronary aneurysm formation was observed following treatment by directional coronary atherectomy. Intravascular ultrasound disclosed that the mechanism involved was plaque rupture. The cause of coronary aneurysm may be multifactorial after coronary interventions. Intravascular ultrasound imaging is useful for understanding the pathologic mechanism of coronary aneurysm production.