Patterning Steps Research Articles

Walking on uneven terrain in healthy adults and the implications for people after stroke.

One third of individuals after stroke report an inability to walk in the community. Community mobility requires walking adaptability - the ability to adjust one's stepping pattern to meet environmental demands and task goals. Walking on uneven terrain (e.g. grass, gravel) has unique requirements and is a critical component of walking adaptability that has not been investigated in the post-stroke population. To summarize current knowledge of biomechanical and neuromuscular modifications during uneven terrain negotiation in healthy individuals and discuss implications of post-stroke impairments. Review of eleven studies, identified through a search of relevant literature on PubMed and CINAHL. On uneven terrain, healthy adults demonstrate numerous gait modifications including a lowered center of mass, increased muscle co-contraction during stance and exaggerated or increased toe clearance during swing. After stroke, changes in muscle activity and limb coordination will likely result in difficulty or inability performing these modifications that healthy adults use to maintain stability and safety when walking on uneven terrain. Studies of biomechanical and neuromuscular control of walking on uneven terrain are needed to quantify mobility limitations in adults post-stroke. Such investigations will contribute to the understanding of mobility impairments after stroke and the design of critically important intervention strategies.

Step Patterns on {100} Faces of Diamond Crystals As-Grown in Mg-Based Systems

In this article, we report the unusual growth of diamond crystals produced in Mg–C and Mg–Ge–C systems at high-pressure, high-temperature conditions. We have found that the growth of the habit {100} faces occurs by deposition of a substance (carbon) on two nonequivalent {100} and {111} surfaces. Precipitation of carbon atoms on the (100) plane occurs by elementary layers with a thickness of about 0.1 and 0.2 nm. The change in the density of elementary steps leads to the formation of step bunches that transform into faceted macrostates with an increase in their thickness of more than 400 nm. The maximum inclination angle of macrostep ends corresponds to the {111} faces position. As a result, singular stable {111} microfacets are formed at the ends of the macrosteps, which themselves grow layer by layer. The deposition of carbon on {100} and {111} surfaces of one simple form of diamond crystals leads to the zonal structure of {100} growth sectors.

Patterns of sedentary time and ambulatory physical activity in a Danish population of girls and women with Rett syndrome

Background: Rett syndrome (RTT) is a rare neurodevelopmental disorder leading to multiple disabilities and high dependency on caregivers. This study aimed to: (1) describe the patterns of sedentary time and daily steps and (2) identify the association of individual and environmental characteristics with sedentary time.Methods: All Danish females with RTT older than 5 years of age and with a MECP2 mutation were invited to participate. The activPAL and StepWatch Activity Monitor (SAM) were worn by participants for at least four days. Sedentary time and step counts were plotted by time to examine daily activity patterns. Associations between sedentary time and individual and environmental covariates were assessed with linear regression models.Results: The median (interquartile range) age of participants was 22.0 (14.3–36.5) years. On average 83.3% (standard deviation 13.9%) of waking hours were spent in sedentary behaviours (n = 48) and the median (interquartile range) daily step count was 5128 (2829–7704) (n = 28). Females older than 33.5 years, and those unable to walk independently were more sedentary.Conclusions: This study demonstrated high levels of sedentary time and low daily step counts in a Danish population of females with RTT. Advancing age and lower walking skills were associated with higher levels of sedentary time.Implications for RehabilitationSedentary lifestyles in individuals with disabilities have a negative impact on health and quality of life.High levels of sedentary time and low daily step counts were demonstrated in a Danish population of females with Rett syndrome.Advancing age and inability to walk independently were strongly associated with higher levels of sedentary time in females with Rett syndrome.Understanding patterns of sedentary behaviour and physical activity can aid health care professionals in developing health-promoting physical activity interventions.

WEARABLE ACTIVITY TRACKERS PROVIDE VALUABLE INSIGHT INTO SEASONAL AND SCHOOL-RELATED PHYSICAL ACTIVITY PATTERNS IN CHILDREN WITH CONGENITAL HEART DISEASE

Objective evaluation of physical activity levels in children with congenital heart disease (CHD) is of increasing interest in the clinical context. Wearable activity trackers have recently been validated in children with CHD. We aimed to illustrate their value to gain insight into activity patterns in children with CHD. We recruited participants (9-18yrs, CHD or cardiac transplant) from pediatric cardiology clinics in BC, Canada. Participants wore an activity tracker for 16 weeks (FitBit Charge HR). In this analysis we included 23 participants who had detailed min-by-min Fitbit data available through the fee-for-service Fitabase. We included days with ≥600 min/day of device wear time, defined based on heart rate signal. For each participant and measurement days, we identified school schedules and obtained climate records in relation to their home. We performed mixed linear regression to assess daily step patterns (adjusting for multiple days per person), and in relation to potential explanatory factors (Stata v.14, p < 0.05). Participants were 14.3±2.3yrs old, 48% were female and 30% were overweight or obese. Ten had mild CHD, 5 moderate CHD, 6 severe CHD and there were 2 cardiac transplant recipients. We included 1,612 valid person-days (mean 70±23 days/person). Loss of days was predominantly due to technical error (loss of min-by-min data due to infrequent device syncing; 32% of possible days); few days had insufficient wear time (5%). Overall, mean daily steps were 9,507+2,243, and 9% of the variance in daily steps were explained by age, sex and diagnosis (mild CHD were least active). Weight status was not related to steps. Twenty-two % of measurement days fell on days during school break, when steps were significantly lower compared with days when school was in session (-1,144 steps/day, p < 0.001). Daily steps were significantly lower on weekends compared with schooldays (-2,446 steps/day, p < 0.001). On school days, approximately 63% of the daily steps were accrued during school hours (8am-4pm). School-based steps were not affected by changes in climate during the measurement period, but there were positive associations between outside temperature and after school/evening steps (4-8pm; p < 0.001), daily steps at the weekend (p=0.045) and daily steps during school break (p=0.021). Wearable activity trackers provide important insight to activity patterns in children with CHD. School is a constant source of physical activity in these children with CHD throughout the year, irrespective of disease severity. In children with low activity levels, school is the primary source of physical activity.

Long-term plate load tests in permafrost region on the Qinghai-Tibetan Plateau

In order to study the deformation behavior of in-situ warm and ice-rich permafrost with seasonally varying ground temperature, two groups of plate load tests were carried out in permafrost region on the Qinghai-Tibetan Plateau. The test results showed that the deformation of the permafrost under a constant load always represented a stepped pattern due to seasonal variation of ground temperature. Affected by the external load and the variation of the ground temperature, both settlement and frost heave occurred. In the long term, however, settlement was the primary characteristic while frost heave was much slight. The settlement rate was positively correlated with load levels, and was greatly affected by soil temperature as well as ice content in the ground. Regardless of frost heave, the deformation curves of permafrost were well expressed by Burgers viscoelasticity model, and the future settlements can be predicted based on the model.

Effects of transcutaneous electrical spinal cord stimulation on stepping patterns during walking

Effects of transcutaneous electrical spinal cord stimulation (tESCS) on the parameters of stepping movements in healthy subjects were investigated during two kinds of activity: walking on a moving treadmill belt (active treadmill) as well as pushing the treadmill belt by effort of the legs (passive treadmill). It was found that the total interference electromyogram (EMG) activity during stepping performance on a passive treadmill was 1.5–2 times higher than during stepping on an active treadmill. In addition, the amplitude of angular displacement of the hip joint and ankle was 2.5 times and 1.7 times higher, respectively, during passive vs. active treadmill, while the duration of stepping cycle decreased by 19%. Although the muscles were exposed to different load and the parameters of motion on the active and passive treadmill were different, tESCS caused an increase in the total EMG activity in 96% of cases both on the active and on the passive treadmill. In both cases, the stepping cycle period decreased by 4–43% in all subjects. These results suggest that tESCS can affect voluntary stepping patterns under conditions of different afferent control.

Effectiveness of a Timing and Coordination Group Exercise Program to Improve Mobility in Community-Dwelling Older Adults

Timing and coordination exercises may be an important addition to community-based health promotion exercise programs to improve walking in older adults. To compare the effectiveness of the On the Move group exercise program, which focuses on the timing and coordination of movement, with a seated strength, endurance, and flexibility program (usual care) at improving function, disability, and walking ability of older adults. Cluster-randomized, single-blind intervention trial. Thirty-two independent living facilities, senior apartment buildings, and senior community centers were randomized to On the Move (16 sites; 152 participants) or usual care (16 sites; 146 participants). Participants were 65 years or older, able to ambulate independently with a gait speed of at least 0.60 m/s, able to follow 2-step commands, and were medically stable. Exercise classes were 50 minutes, twice a week for 12 weeks and had 10 or fewer participants per class. On the Move consisted of warm-up, timing and coordination (stepping and walking patterns), strengthening, and stretching exercises. The usual-care program consisted of warm-up, strength, endurance, and stretching exercises. The primary outcomes were self-report of function and disability (Late Life Function and Disability Instrument) and mobility (6-minute walk distance and gait speed) assessed by blinded individuals. Participants (mean [SD] age, 80.0 [8.1] years) were mostly female (251 [84.2%]) and white (249 [83.6%]) and had a mean (SD) of 2.8 (1.4) chronic conditions. Intervention groups were similar on baseline characteristics. Postintervention, 142 (93.4%) participants in On the Move and 139 (95.2%) participants in usual care completed testing. On the Move had greater mean (SD) improvements than the usual-care group in gait speed (0.05 [0.13] vs -0.01 [0.11] m/s; adjusted difference = 0.05 [0.02] m/s; P = .002) and 6-minute walk distance (20.6 [57.1] vs 4.1 [55.6] m; adjusted difference = 16.7 [7.4] m; P = .03). Attendance was greater in the usual-care program compared with On the Move (95 [65.1%] vs 76 [50.0%] attended ≥20 classes; P = .03). There were no significant differences in any of the other primary or secondary outcomes. The On the Move group exercise program was more effective at improving mobility than a usual-care exercise program, despite lower attendance. Additional research examining the impact of the intervention on long-term disability outcomes is needed before recommending routine implementation into clinical practice. clinicaltrials.gov Identifier: NCT01986647.

Feasibility study design and methods for a home-based, square-stepping exercise program among older adults with multiple sclerosis: The SSE-MS project.

We propose a randomized controlled trial (RCT) examining the feasibility of square-stepping exercise (SSE) delivered as a home-based program for older adults with multiple sclerosis (MS). We will assess feasibility in the four domains of process, resources, management and scientific outcomes. The trial will recruit older adults (aged 60 years and older) with mild-to-moderate MS-related disability who will be randomized into intervention or attention control conditions. Participants will complete assessments before and after completion of the conditions delivered over a 12-week period. Participants in the intervention group will have biweekly meetings with an exercise trainer in the Exercise Neuroscience Research Laboratory and receive verbal and visual instruction on step patterns for the SSE program. Participants will receive a mat for home-based practice of the step patterns, an instruction manual, and a logbook and pedometer for monitoring compliance. Compliance will be further monitored through weekly scheduled Skype calls. This feasibility study will inform future phase II and III RCTs that determine the actual efficacy and effectiveness of a home-based exercise program for older adults with MS.

An automatic glioma grading method based on multi-feature extraction and fusion.

An accurate assessment of tumor malignancy grade in the preoperative situation is important for clinical management. However, the manual grading of gliomas from MRIs is both a tiresome and time consuming task for radiologists. Thus, it is a priority to design an automatic and effective computer-aided diagnosis (CAD) tool to assist radiologists in grading gliomas. To design an automatic computer-aided diagnosis for grading gliomas using multi-sequence magnetic resonance imaging. The proposed method consists of two steps: (1) the features of high and low grade gliomas are extracted from multi-sequence magnetic resonance images, and (2) then, a KNN classifier is trained to grade the gliomas. In the feature extraction step, the intensity, volume, and local binary patterns (LBP) of the gliomas are extracted, and PCA is used to reduce the data dimension. The proposed "Intensity-Volume-LBP-PCA-KNN" method is validated on the MICCAI 2015 BraTS challenge dataset, and an average grade accuracy of 87.59% is obtained. The proposed method is an effective method for automatically grading gliomas and can be applied to real situations.

Extract-and-match geometric corner and step pattern approach for registration of fluoroscopic X-ray sequences.

This paper presents a method to extract-and-match robust corner features based on connecting edges from the edge maps, mainly formed by coronary vascular junctions in fluoroscopic x-ray sequence images. Such images are challenging due to the aperture problem. To overcome this, existing approaches attempt to extract vessels for registration. However, they are ineffective in poor quality images. Our approach describes the extracted robust corner features in a rotation invariant manner using step patterns, followed by matching them effectively. Experimental results show that our approach performs very well (above 80%) in a dataset of poor quality fluoroscopic x-ray image sequences without extensive processing such as segmentation or learning.

Large area nanoimprint by substrate conformal imprint lithography (SCIL)

Abstract Releasing the potential of advanced material properties by controlled structuring materials on sub-100-nm length scales for applications such as integrated circuits, nano-photonics, (bio-)sensors, lasers, optical security, etc. requires new technology to fabricate nano-patterns on large areas (from cm2 to 200 mm up to display sizes) in a cost-effective manner. Conventional high-end optical lithography such as stepper/scanners is highly capital intensive and not flexible towards substrate types. Nanoimprint has had the potential for over 20 years to bring a cost-effective, flexible method for large area nano-patterning. Over the last 3–4 years, nanoimprint has made great progress towards volume production. The main accelerator has been the switch from rigid- to wafer-scale soft stamps and tool improvements for step and repeat patterning. In this paper, we discuss substrate conformal imprint lithography (SCIL), which combines nanometer resolution, low patterns distortion, and overlay alignment, traditionally reserved for rigid stamps, with the flexibility and robustness of soft stamps. This was made possible by a combination of a new soft stamp material, an inorganic resist, combined with an innovative imprint method. Finally, a volume production solution will be presented, which can pattern up to 60 wafers per hour.

Split-arm swinging: the effect of arm swinging manipulation on interlimb coordination during walking.

Human locomotion is defined by bilateral coordination of gait (BCG) and shared features with the fore-hindlimb coordination of quadrupeds. The objective of the present study is to explore the influence of arm swinging (AS) on BCG. Sixteen young, healthy individuals (eight women; eight right motor-dominant, eight left-motor dominant) participated. Participants performed 10 walking trials (2 min). In each of the trials AS was unilaterally manipulated (e.g., arm restriction, weight on the wrist), bilaterally manipulated, or not manipulated. The order of trials was random. Walking trials were performed on a treadmill. Gait kinematics were recorded by a motion capture system. Using feedback-controlled belt speed allowed the participants to walk at a self-determined gait speed. Effects of the manipulations were assessed by AS amplitudes and the phase coordination index (PCI), which quantifies the left-right anti-phased stepping pattern. Most of the AS manipulations caused an increase in PCI values (i.e., reduced lower limb coordination). Unilateral AS manipulation had a reciprocal effect on the AS amplitude of the other arm such that, for example, over-swinging of the right arm led to a decrease in the AS amplitude of the left arm. Side of motor dominance was not found to have a significant impact on PCI and AS amplitude. The present findings suggest that lower limb BCG is markedly influenced by the rhythmic AS during walking. It may thus be important for gait rehabilitation programs targeting BCG to take AS into account.NEW & NOTEWORTHY Control mechanisms for four-limb coordination in human locomotion are not fully known. To study the influence of arm swinging (AS) on bilateral coordination of the lower limbs during walking, we introduced a split-AS paradigm in young, healthy adults. AS manipulations caused deterioration in the anti-phased stepping pattern and impacted the AS amplitudes for the contralateral arm, suggesting that lower limb coordination is markedly influenced by the rhythmic AS during walking.

Increasing Human Neural Stem Cell Transplantation Dose Alters Oligodendroglial and Neuronal Differentiation after Spinal Cord Injury.

SummaryMultipotent human central nervous system-derived neural stem cells transplanted at doses ranging from 10,000 (low) to 500,000 (very high) cells differentiated predominantly into the oligodendroglial lineage. However, while the number of engrafted cells increased linearly in relationship to increasing dose, the proportion of oligodendrocytic cells declined. Increasing dose resulted in a plateau of engraftment, enhanced neuronal differentiation, and increased distal migration caudal to the transplantation sites. Dose had no effect on terminal sensory recovery or open-field locomotor scores. However, total human cell number and decreased oligodendroglial proportion were correlated with hindlimb girdle coupling errors. Conversely, greater oligodendroglial proportion was correlated with increased Ab step pattern, decreased swing speed, and increased paw intensity, consistent with improved recovery. These data suggest that transplant dose, and/or target niche parameters can regulate donor cell engraftment, differentiation/maturation, and lineage-specific migration profiles.

Examining Fifth-Grade In-School Physical Activity Patterns

PURPOSE: The purpose of the study was to determine the minimum number of days necessary to estimate mean physical activity levels, as both moderate-to-vigorous physical activity (MVPA) and steps per day, in fifth-grade students using objective physical activity monitors across two semesters. METHODS: Activity patterns were assessed during two school semesters, spring (N = 82 boys & 84 girls) and fall (N = 89 boys & 91 girls), from 10-12 year old fifth-grade students in four Midwestern elementary schools. Data was collected using wrist worn activity trackers. The devices were administered by teachers at the start of each school day and collected at the end of each school day for two consecutive weeks. Monitors measured MVPA and steps per day. Demographic and anthropometric data were also recorded (age, height, weight). All data was uploaded to the monitor’s manufacturer website and then collected by the researchers. Steps and MVPA were examined, individually, with Cronbach’s alpha to determine how many days of measurement were needed to assess mean activity patterns. RESULTS: The reliability analysis suggested that at least four days of measurement were needed to achieve an alpha of 0.80 for both steps (α = 0.825, 95% CI [0.777-0.865]) and MVPA (α = 0.839, 95% CI [0.795-0.87]) during spring collection. During the fall semester, at least four days were also necessary to achieve a reliability of 0.80 in steps (α = 0.803, 95% CI [0.751-0.846]) and MVPA (α = 0.811, 95% CI [0.761-0.852]). However, fall five-day activity patterns did exhibit greater variability than four-day activity patterns in both steps (α = 0.784, 95% CI [0.730-0.830]) and MVPA (α = 0.794, 95% CI [0.742-0.838]). CONCLUSIONS: These results indicate that four-day activity monitoring protocols most accurately estimate the mean in-school physical activity patterns, steps and MVPA, in fifth grades students. It should be noted that the results indicate consistency was not improved by a fifth day of measurement in steps and MVPA during a five-day collection period.

HealtheBrain: an innovative smartphone application to improve cognitive function in older adults.

Exercise-based interventions have shown promise in slowing cognitive decline, however there is limited evidence for scalability. Our previous research has linked a novel visuospatial memory exercise intervention, incorporating patterned walking or square-stepping exercise (SSE) with significant improvements in executive function and memory among older adults with normal cognition as well as those with subjective cognitive complaints (SCC) and mild cognitive impairment (MCI). The aim of the current study was to determine the feasibility and utility of the HealtheBrain smartphone app to deliver SSE outside the laboratory among older adults with and without cognitive impairment. Previous healthy research subjects with and without SCC or MCI, who had previous exposure to SSE, and who owned or had access to an iPhone of iPad, were recruited to download the HealtheBrain app and use it up to 3 weeks. There were no restrictions on the number of times subjects could use the app. A 15-question survey was developed to assess feasibility and utility of the HealtheBrain app and completed online following the brief exposure period. Of 135 people who were identified, 95 were contacted between September 2014 to August 2015, 27 downloaded the HealtheBrain app on their iPhone or iPad from the App Store and 19 completed the questionnaire. Subjects (n=19) were an average age of 68.3±5.4; 74% female and had 15.5±2.8 years of education (84% post-secondary education), a mean Mini Mental State examination score of 29.1 (SD 1.2) out of 30 and Montreal Cognitive Assessment score of 26.3 (SD 1.9) out of 30. Subjects used the HealtheBrain app 1-7 days per week, mostly at home. Of possible stages of progression, subjects mainly used the stage 1 and 2 beginner patterns. Subjects reported perceived and technical challenges registering horizontal step patterns associated with stage 2 and greater progression. Sixty percent found the app was easy to use or similar to what they experienced with SSE in the laboratory setting. Most said they would continue to use the HealtheBrain app and would recommend it to friends and family. The HealtheBrain app was feasible in providing SSE to older adults with the appropriate smartphone device outside the laboratory setting. Challenges were identified with perceived capture of higher levels of SSE stages that used horizontal step patterns. This as well as technical issues with horizontal step patterns will be addressed by newer GPS technology in current smartphone devices. Most subjects stated they would continue to use the HealtheBrain app and refer to their friends and family. We believe that our findings in a representative cohort support the HealtheBrain app as a scalable intervention to promote cognitive health in older adults.

Spatial-temporal Evolution of Coupling Coordination between Socio-economic Development and Growth of Service Economy—A Case Study in Zhejiang Province

Based on the analysis of coupling mechanism between socio-economic growth and the growth of service economy, this paper reconstructed the evaluation index system of regional socio-economic development and service economic growth, then obtained comprehensive evaluation index of regional socio-economic development and the growth of service economy by using entropy method. On the use of coupling coordination model, this paper measured the coupling development of socio-economic development and the growth of service economy in Zhejiang Province, and carried out spatial econometric analysis of coupling coordination degree of different regions. Main conclusions are as follows: the coupling coordination degree of socio-economic growth and service economic growth in Zhejiang Province was growing during 2002-2012. At the meantime, the spatial region variation of coupling coordination degree was changing constantly. The internal constitution of high level and low-level areas were changing obviously. In addition, the coupling coordination degree of socio-economic growth and the growth of service economy in Zhejiang Province shows agglomeration trend, and clearly showing the stepped spatial pattern of “high in northeast and low in southwest”.

Two mechanisms forming a comblike step pattern induced by a moving linear adatom source.

We carry out phase field simulations to study properties of the comblike step patterns induced by an adatom source. When an adatom source advances right in front of a step, step wandering is caused by the asymmetry of the surface diffusion field and small protrusions are formed. If the velocity of the source V_{p} is smaller than a critical value V_{p}^{c}, the protrusions follow the adatom source with coarsening of the step pattern, and a regular comblike pattern with finger-like protrusions is formed. With a sufficiently small V_{p}, the gap of the supersaturation is large at the adatom source. Since the period of protrusions, Λ, decreases with increasing V_{p}, the coarsening of step pattern is irrelevant for the protrusions to catch up with the adatom source. Near V_{p}^{c}, the gap of the supersaturation at the adatom source is small. Taking account of the increase in Λ with increasing V_{p}, the coarsening of the step pattern is essential for the protrusions to follow the adatom source.

Learning new sequential stepping patterns requires striatal plasticity during the earliest phase of acquisition.

Animals including humans execute motor behavior to reach their goals. For this purpose, they must choose correct strategies according to environmental conditions and shape many parameters of their movements, including their serial order and timing. To investigate the neurobiology underlying such skills, we used a multi-sensor equipped, motor-driven running wheel with adjustable sequences of foothold pegs on which mice ran to obtain water reward. When the peg patterns changed from a familiar pattern to a new pattern, the mice had to learn and implement new locomotor strategies in order to receive reward. We found that the accuracy of stepping and the achievement of water reward improved with the new learning after changes in the peg-pattern, and c-Fos expression levels assayed after the first post-switch session were high in both dorsolateral striatum and motor cortex, relative to post-switch plateau levels. Combined insitu hybridization and immunohistochemistry of striatal sections demonstrated that both enkephalin-positive (indirect pathway) neurons and substance P-positive (direct pathway) neurons were recruited specifically after the pattern switches, as were interneurons expressing neuronal nitric oxide synthase. When we blocked N-methyl-D-aspartate (NMDA) receptors in the dorsolateral striatum by injecting the NMDA receptor antagonist, D-2-amino-5-phosphonopentanoic acid (AP5), we found delays in early post-switch improvement in performance. These findings suggest that the dorsolateral striatum is activated on detecting shifts in environment to adapt motor behavior to the new context via NMDA-dependent plasticity, and that this plasticity may underlie forming and breaking skills and habits as well as to behavioral difficulties in clinical disorders.

Structural Characterization of Vascular Endothelial Growth Factor by Solid-State Nanopores

A novel solid-state nanopore sensing technique is described to study vascular endothelial growth factor (VEGF). VEGF is a cytokine that stimulates vascularization and is used as a cancer biomarker. Its biological activity depends on the isomerization state. Dimeric VEGF facilitates dimerization of the VEGF receptor which initiates the signal transduction pathway. Monomeric VEGF consists of two domains; a VEGF receptor recognition domain and a heparin binding domain, separated by a peptide sequence cleavable by plasmin. Translocation of VEGF through a 4 to 6 nm-diameter pore, fabricated via transmission electron microscope sculpting on an thinned 10 nm free-standing SiN membrane, produces a structural-dependent electronic signature. By fine-tuning the pore's geometry and experimental conditions, VEGF translocation consistently produces multi-step patterns, which are used to differentiate monomeric and dimeric isoforms. The equilibrium dissociation constant depends on concentration and pH. Further study with TCEP and plasmin show that the step pattern corresponds to the translocation of individual protein domains. These results demonstrate the potential for nanopores to detect small proteins and its capability to resolve the higher-order structure of proteins at the single-molecule level.

Kinematics of the Lever Arm Swing in Myosin VI

Similarly to other myosins, Myosin VI (MVI) uses the energy stored in ATP to move on the actin filament. During the power stroke, a structural transition initiated in the motor domain leads to the movement of the converter, which is exaggerated by the swinging lever arm. MVI, like Myosin V, can form dimers that walk processively on actin. The uniqueness of MVI emerges from the details of its motion: MVI walks towards the pointed end of the actin filament, and it does so undergoing an erratic stepping pattern, in which backward steps are combined with hand-over-hand and inchworm-like forward steps. Experimental evidence suggested that the lever arm of the leading head of a MVI dimer is uncoupled from the motor domain. We developed a model of the power stroke of MVI and we show that it occurs in two steps: first the motor domain, including the converter, reaches the post-stroke conformation without directing the lever arm forward. Secondly, the lever arm undergoes a diffusion towards its post-stroke orientation, which is only weakly biased by the motor domain. The uncoupling of the lever arm during the power stroke occurs even without backward load, suggesting that it is a mechanism encoded in MVI strucutre. Also, a backward load compatible with the largest estimated interhead tension in a MVI dimer prevents the second step of the power stroke, suggesting that a MVI dimer leading head lever arm is uncoupled from the motor domain. Our model, without any adjustable parameters, provides results that are in quantitative agreement with polTIRF experiments monitoring the orientation of a calmodulin-bound probe, and they suggest that the two-step mechanism with an uncoupled lever arm might contribute to explaining the experimentally-observed combination of hand-over-hand and inchworm-like steps.