Concept: Electric motor
Diverse high-torque bacterial flagellar motors assemble wider stator rings using a conserved protein scaffold
- Proceedings of the National Academy of Sciences of the United States of America
- Published over 4 years ago
Although it is known that diverse bacterial flagellar motors produce different torques, the mechanism underlying torque variation is unknown. To understand this difference better, we combined genetic analyses with electron cryo-tomography subtomogram averaging to determine in situ structures of flagellar motors that produce different torques, from Campylobacter and Vibrio species. For the first time, to our knowledge, our results unambiguously locate the torque-generating stator complexes and show that diverse high-torque motors use variants of an ancestrally related family of structures to scaffold incorporation of additional stator complexes at wider radii from the axial driveshaft than in the model enteric motor. We identify the protein components of these additional scaffold structures and elucidate their sequential assembly, demonstrating that they are required for stator-complex incorporation. These proteins are widespread, suggesting that different bacteria have tailored torques to specific environments by scaffolding alternative stator placement and number. Our results quantitatively account for different motor torques, complete the assignment of the locations of the major flagellar components, and provide crucial constraints for understanding mechanisms of torque generation and the evolution of multiprotein complexes.
Understanding the evolution of molecular machines underpins our understanding of the development of life on earth. A well-studied case are bacterial flagellar motors that spin helical propellers for bacterial motility. Diverse motors produce different torques, but how this diversity evolved remains unknown. To gain insights into evolution of the high-torque ε-proteobacterial motor exemplified by the Campylobacter jejuni motor, we inferred ancestral states by combining phylogenetics, electron cryotomography, and motility assays to characterize motors from Wolinella succinogenes, Arcobacter butzleri and Bdellovibrio bacteriovorus. Observation of ~12 stator complexes in many proteobacteria, yet ~17 in ε-proteobacteria suggest a “quantum leap” evolutionary event. Campylobacter-type motors have high stator occupancy in wider rings of additional stator complexes that are scaffolded by large proteinaceous periplasmic rings. We propose a model for motor evolution wherein independent inner- and outer-membrane structures fused to form a scaffold for additional stator complexes. Significantly, inner- and outer-membrane associated structures have evolved independently multiple times, suggesting that evolution of such structures is facile and poised the ε-proteobacteria to fuse them to form the high-torque Campylobacter-type motor.
There are many challenges to measuring power input and force output from a flapping vertebrate. Animals can vary a multitude of kinematic parameters simultaneously, and methods for measuring power and force are either not possible in a flying vertebrate or are very time and equipment intensive. To circumvent these challenges, we constructed a robotic, multi-articulated bat wing that allows us to measure power input and force output simultaneously, across a range of kinematic parameters. The robot is modeled after the lesser dog-faced fruit bat, Cynopterus brachyotis, and contains seven joints powered by three servo motors. Collectively, this joint and motor arrangement allows the robot to vary wingbeat frequency, wingbeat amplitude, stroke plane, downstroke ratio, and wing folding. We describe the design, construction, programing, instrumentation, characterization, and analysis of the robot. We show that the kinematics, inputs, and outputs demonstrate good repeatability both within and among trials. Finally, we describe lessons about the structure of living bats learned from trying to mimic their flight in a robotic wing.
Our world is increasingly powered by electricity, which is largely converted to or from mechanical energy using electric motors. Several applications have driven the miniaturization of these machines, resulting in high rotational speeds. Although speeds of several hundred thousand revolutions per minute have been used industrially, we report the realization of an electrical motor reaching 40 million rpm to explore the underlying physical boundaries. Millimeter-scale steel spheres, which are levitated and accelerated by magnetic fields inside a vacuum, are used as a rotor. Circumferential speeds exceeding 1000 m/s and centrifugal accelerations of more than 4 × 108 times gravity were reached. The results open up new research possibilities, such as the testing of materials under extreme centrifugal load, and provide insights into the development of future electric drive systems.
The magnetically suspended Control Moment Gyroscope (CMG) has the advantages of long-life, micro-vibration and being non-lubricating, and is the ideal actuator for agile maneuver satellite attitude control. However, the stability of the rotor in magnetic bearing and the precision of the output torque of a magnetically suspended CMG are affected by the rapid maneuvers of satellites. In this paper, a dynamic model of the agile satellite including a magnetically suspended single gimbal control moment gyroscope is built and the equivalent disturbance torque effected on the rotor is obtained. The feedforward compensation control method is used to depress the disturbance on the rotor. Simulation results are given to show that the rotor displacement is obviously reduced.
The bacterial flagellar motor, one of the few rotary motors in nature, produces torque to drive the flagellar filament by ion translocation through membrane-bound stator complexes. We used the light-driven proton pump proteorhodopsin (pR) to control the proton-motive force (PMF) in vivo by illumination. pR excitation was shown to be sufficient to replace native PMF generation, and when excited in cells with intact native PMF generation systems increased motor speed beyond the physiological norm. We characterized the effects of rapid in vivo PMF changes on the flagellar motor. Transient PMF disruption events from loss of illumination caused motors to stop, with rapid recovery of their previous rotation rate after return of illumination. However, extended periods of PMF loss led to stepwise increases in rotation rate upon PMF return as stators returned to the motor. The rate constant for stator binding to a putative single binding site on the motor was calculated to be 0.06 s(-1) . Using GFP-tagged MotB stator proteins, we found that transient PMF disruption leads to reversible stator diffusion away from the flagellar motor, showing that PMF presence is necessary for continued motor integrity, and calculated a stator dissociation rate of 0.038 s(-1) .
BACKGROUND: There is a paucity of data concerning the energy requirements (ERs) of preschool-age children with cerebral palsy (CP), the knowledge of which is essential for early nutritional management. OBJECTIVE: We aimed to determine the ERs for preschool-age children with CP in relation to functional ability, motor type, and distribution and compared with typically developing children (TDC) and published estimation equations. DESIGN: Thirty-two children with CP (63% male) of all functional abilities, motor types, and distributions and 16 TDC (63% male) aged 2.9-4.4 y participated in this study. The doubly labeled water method was used to determine ERs. Statistical analyses were conducted by 1-factor ANOVA and post hoc Tukey honestly significant difference tests, independent and paired t tests, Bland and Altman analyses, correlations, and multivariable regressions. RESULTS: As a population, children with CP had significantly lower ERs than did TDC (P < 0.05). No significant difference in ERs was found between ambulant children and TDC. Marginally ambulant and nonambulant children had ERs that were ∼18% lower than those of ambulant children and 31% lower than those of TDC. A trend toward lower ERs with greater numbers of limbs involved was observed. The influence of motor type could not be determined statistically. Published equations substantially underestimated ERs in the nonambulant children by ∼22%. CONCLUSIONS: In preschool-age children with CP, ERs decreased as ambulatory status declined and more limbs were involved. The greatest predictor of ERs was fat-free mass, then ambulatory status. Future research should build on the information presented to expand the knowledge base regarding ERs in children with CP. This trial was registered with the Australian New Zealand Clinical Trials Registry as ACTRN 12612000686808.
To obtain high dynamic performance on induction motor drives (IMD), variable voltage and variable frequency operation has to be performed by measuring speed of rotation and stator currents through sensors and fed back them to the controllers. When the sensors are undergone a fault, the stability of control system, may be designed for an industrial process, is disturbed. This paper studies the negative effects on a 12.5 hp induction motor drives when the field oriented control system is subjected to sensor faults. To illustrate the importance of this study mine hoist load diagram is considered as shaft load of the tested machine. The methods to recover the system from sensor faults are discussed. In addition, the various speed sensorless schemes are reviewed comprehensively.
Multi-finger operations provide realistic and natural methods when interacting with remote or virtual environment. Hence, haptic devices with multi-finger input are highly desirable. MR (Magneto-rheological) actuators are preferable options in haptics, because they can produce larger passive torque and have larger torque-volume ratios than the conventional actuators. Among the existing haptic MR actuators, most of them are still bulky and heavy. If they were smaller and lighter, they would become more suitable for haptics. In this paper, a small-scale yet powerful MR actuator was designed to build a multi-finger interface for the 6 DOF haptic device. The compact structure was achieved by adopting the multi-disc configuration. Based on this configuration, the MR actuator can generate the maximum torque of 480 N.mm with dimensions of only 36 mm diameter and 18 mm height. Performance evaluation showed that it can exhibit a relatively high dynamic range and good response characteristics when compared with some other haptic MR actuators. The multi-finger interface is equipped with three MR actuators and can provide up to 8 N passive force to the thumb, index and middle fingers, respectively. An application example was used to demonstrate the effectiveness and potential of this new MR actuator based interface.
The bacterial flagellar motor consists of a rotor and a dozen stator units and regulates the number of active stator units around the rotor in response to changes in the environment. The MotPS complex is a Na(+)-type stator unit in the Bacillus subtilis flagellar motor and binds to the peptidoglycan layer through the peptidoglycan-binding (PGB) domain of MotS to act as the stator. The MotPS complex is activated in response to an increase in the Na(+) concentration in the environment, but the mechanism of this activation has remained unknown. We report that activation occurs by a Na(+)-induced folding and dimer formation of the PGB domain of MotS, as revealed in real-time imaging by high-speed atomic force microscopy. The MotPS complex showed two distinct ellipsoid domains connected by a flexible linker. A smaller domain, corresponding to the PGB domain, became structured and unstructured in the presence and absence of 150 mM NaCl, respectively. When the amino-terminal portion of the PGB domain adopted a partially stretched conformation in the presence of NaCl, the center-to-center distance between these two domains increased by up to 5 nm, allowing the PGB domain to reach and bind to the peptidoglycan layer. We propose that assembly of the MotPS complex into a motor proceeds by means of Na(+)-induced structural transitions of its PGB domain.