Kinesins are motor proteins that convert chemical energy from ATP hydrolysis into mechanical energy used to generate force along microtubules, transporting organelles, vesicles, and proteins within the cell. Kar3 kinesins are microtubule minus-end-directed motors with pleiotropic functions in mating and mitosis of budding and fission yeast. In Saccharomyces cerevisiae, Kar3 is multifunctionalized by two non-catalytic companion proteins, Vik1 and Cik1. A Kar3-like kinesin and a single Vik1/Cik1 ortholog are also expressed by the filamentous fungus Ashbya gossypii, which exhibits different nuclear movement challenges and unique microtubule dynamics from its yeast relatives. We hypothesized that these differences in A. gossypii physiology could translate into interesting and novel differences in its versions of Kar3 and Vik1/Cik1. Presented here is a structural and functional analysis of recombinantly expressed and purified forms of these motor proteins. Compared to the previously published S. cerevisiae Kar3 motor domain structure (ScKar3MD), AgKar3MD displays differences in the conformation of the ATPase pocket. Perhaps it is not surprising then that we observed the maximal microtubule-stimulated ATPase rate (kcat) of AgKar3MD to be approximately 3-fold slower than ScKar3MD, and that the affinity of AgKar3MD for microtubules (Kd,MT) was lower than ScKar3MD. This may suggest that elements that compose the ATPase pocket and that participate in conformational changes required for efficient ATP hydrolysis or products release work differently for AgKar3 and ScKar3. There are also subtle structural differences in the disposition of the secondary structural elements in the small lobe (B1a, B1b, and B1c) at the edge of the motor domain of AgKar3 that may reflect the enhanced microtubule-depolymerization activity that we observed for this motor, or they could relate to its interactions with a different regulatory companion protein than its budding yeast counterpart. Although we were unable to gain experimentally determined high-resolution information of AgVik1, the results of Phyre2-based bioinformatics analyses may provide a structural explanation for the limited microtubule-binding activity we observed. These and other fundamental differences in AgKar3/Vik1 could explain divergent functionalities from the ScKar3/Vik1 and ScKar3/Cik1 motor assemblies. / Thesis (Master, Biochemistry) -- Queen's University, 2012-07-26 10:40:54.738

When one learns a novel motor skill, retention of that skill requires consolidation of motor learning. Previous reports have shown that preceding sessions of motor learning can interfere with the acquisition of new tasks and that new motor learning can disrupt previously retained skills. A recent study by Caithness et al. (2004) shows that new learning, even after long delays, can totally disrupt prior retention. This finding is consistent with the idea that re-activated memories become labile and subject to displacement. However the result is difficult to reconcile with day-to-day experience in which skills improve with repetition and are not disrupted by unrelated activities. In this experiment, we show that when subjects learn new dynamics the influence of one task on another depends on the similarity of the force fields involved. We used a robotic manipulandum to define environments in which subjects learned to move. We used an AB design in which subjects learned field A on day one and B on day 2. We show that the effect of having learned environment A 24-hours prior to learning B varies along a continuum from facilitation when they are identical, through little effect when they are unrelated, to total interference when they are opposite. These findings thus indicate that the nervous system encodes information about dynamics in a fashion that is predictable on the basis of the similarity between the initial and final training environments. One month following their initial training, we tested subjects environment C, whose dynamics were opposite to B. Performance on this task suggests that the nervous system retained neither discrete instances of past training nor solely the most recent motor learning, but instead constructed a running average of learned dynamics to build an individual's motor repertoire.

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When bi-lateral movements of differing difficulty are performed as rapidly as possible the "easier" of the two limbs slows down and is attracted to the temporal structure of the more difficult movement. Simultaneous movements are expected to be severely compromised in Parkinson's Disease (PD). The purpose of this study was to investigate whether Parkinsonians elicit temporal assimilations in the belief that an assimilatory response may facilitate simultaneous bi-lateral control in PD. / Temporal attractions were elicited by the non-impaired subjects during the bi-lateral task. The increased movement duration of the "easy" limb was the consequence of a contralateral motor command interference. The Parkinsonians failed to generate sufficient contralateral shoulder torque to interfere with the metrical structure of the "easier" task comprising the bi-lateral movements. These observations suggest that temporal assimilations elicited by this class of movements are the result of a motor command interference and not the effect of a restructuring of the movements metrics.

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The principal theories of human motor skill are compared. Disagreements between them centre around the exact details of the feedback loops used for control. In order to throw some light on this problem a commonplace skill was analysed using computer techniques to both record and model the movement. Bicycle riding was chosen as an example because it places strict constraints on the freedom of the rider's actions and consequently allows a fairly simple model to be used. Given these constraints a faithful record of the delicate balancing movements of the handlebar must also be a record of the rider's actions in controlling the machine. An instrument pack, fitted with gyroscopic sensors and a handlebar potentiometer, recorded the roll, yaw and steering angle changes during free riding in digital form on a microcomputer disc. A discrete step computer model of the rider and machine was used to compare the output characteristic of various control systems with that of the experimental subjects. Since the normal bicycle design gives a measure of automatic stability it is not possible to tell how much of the handlebar movement is due to the rider and how much to the machine. Consequently a bicycle was constructed in which the gyroscopic and castor stability were removed. In order to reduce the number of sensory contributions the subjects were blindfolded. The recordings showed that the-basic method of control was a combination of a continuous delayed repeat of the roll angle rate in the handle-bar channel, with short intermittent ballistic acceleration inputs to control angle of lean and consequently direction., A review of the relevant, literature leads to the conclusion that the proposed control system is consistent with current physiological knowledge. Finally the bicycle control system discovered in the experiments is related to the theories of motor skills discussed in the second chapter.

This Thesis is about the application of Statistical Energy Analysis (SEA) to the study of noise and vibration in motor vehicles. Methods for predicting the transmission of structural waves between body panels in motor cars are given. A complex joint technique based on the wave dynamic stiffness approach is discussed in detail. This technique can account for the complexities of the joint structures found in motor vehicles. Transmission of vibration energy between panels connected by a curved section of panel has been investigated using the complex joint modelling technique. Wave Intensity Analysis(WIA) and SEA were used to calculate the coupled panel vibration levels based on transmission coefficients calculated using the complex joint techniques. Energy Level Differences (ELDs) were measured for comparison with predicted results using laboratory models. SEA failed to accurately predict the ELDs except at low frequencies. However WIA was able to predicted the ELDs with reasonable accuracy using an existing expression for transmission at a panel corner joint. Two SEA models of a small passenger car have also been constructed. One assumes simpler joint configurations when calculating transmission coefficients and the other uses the complex joint technique. Panel ELDs were measured using a small passenger car. The SEA model using the complex joint method gives better agreement with measured ELDs than did the model using the simpler joints. saloon Sound Pressure Level (SPL) as a result of engine noise was measured. Both SEA models of the vehicle gave good agreement between measured and predicted Saloon SPL. A noise problem associated with exhaust misalignment is also investigated.