Structure and Function in Homodimeric Enzymes:Simulations of Cooperative and Independent Functional Motions

Large-scale conformational change is a common feature in the catalytic cycles of enzymes. Many enzymes function as homodimers with active sites that contain elements from both chains. Symmetric and anti-symmetric cooperative motions in homodimers can potentially lead to correlated active site opening and/or closure, likely to be important for ligand binding and release. Here, we examine such motions in two different domain-swapped homodimeric enzymes: the DcpS scavenger decapping enzyme and citrate synthase. We use and compare two types of all-atom simulations: conventional molecular dynamics simulations to identify physically meaningful conformational ensembles, and rapid geometric simulations of flexible motion, biased along normal mode directions, to identify relevant motions encoded in the protein structure. The results indicate that the opening/closure motions are intrinsic features of both unliganded enzymes. In DcpS, conformational change is dominated by an anti-symmetric cooperative motion, causing one active site to close as the other opens; however a symmetric motion is also significant. In CS, we identify that both symmetric (suggested by crystallography) and asymmetric motions are features of the protein structure, and as a result the behaviour in solution is largely non-cooperative. The agreement between two modelling approaches using very different levels of theory indicates that the behaviours are indeed intrinsic to the protein structures. Geometric simulations correctly identify and explore large amplitudes of motion, while molecular dynamics simulations indicate the ranges of motion that are energetically feasible. Together, the simulation approaches are able to reveal unexpected functionally relevant motions, and highlight differences between enzymes

Goalkeeping in the soccer penalty kick: it is time we take affordance-based control seriously!

The goalkeeper’s difficulty in the soccer penalty kick originates from the extreme spatiotemporal constraints of the situation. The present review claims that the current understanding is biased toward attributing a goalkeeper’s success in saving a penalty kick to perceptual-cognitive skill. To investigate the goalkeeper’s skill, researchers have often adopted video tasks. In doing so, they studied perceptual skill in isolation from action. We use affordance-based control theory to propose an alternative understanding and research methodology. We argue that goalkeepers in the penalty kick situation should regulate their actions in ways that sustain the perception of stoppability. To capture this, we outline the building blocks for a required lateral velocity model, in which the goalkeepers’ required actions are scaled to their maximum capabilities. In doing so, we provide new directions for research

A novel on-field training intervention improves novice goalkeeper penalty kick performance

This study developed an on-field anticipation training intervention with the aim of improving novice goalkeeper penalty kick performance. Eighteen participants were allocated to either one-player (OP); or three-player (TP) training. The OP group faced “traditional” practice, with one player running-up to execute each kick. The TP group faced three players in a form of variable practice; two players stopped their run-up approximately 1.2m from the ball with the third-player executing the kick. Following training, results revealed that TP made significantly more saves when facing non-deception kicks in comparison with OP. An implication for applied practice is that there are potential gains to be made through training anticipation skills via new on-field practices rather than the current research focus on video-based training

Touchscreen Pointing and Swiping:The Effect of Background Cues and Target Visibility

By assessing the precision of gestural interactions with touchscreen targets, the authors investigate how the type of gesture, target location, and scene visibility impact movement endpoints. Participants made visually and memory-guided pointing and swiping gestures with a stylus to targets located in a semicircle. Specific differences in aiming errors were identified between swiping and pointing. In particular, participants overshot the target more when swiping than when pointing and swiping endpoints showed a stronger bias toward the oblique than pointing gestures. As expected, the authors also found specific differences between conditions with and without delays. Overall, the authors observed an influence on movement execution from each of the three parameters studied and uncovered that the information used to guide movement appears to be gesture specific

The differential effects of task difficulty on the perception of passing distance and subsequent passing action in a field hockey push pass task

The aims of the study were to initially investigate whether the perceived distance of a field hockey push pass task was influenced by manipulating task difficulty (Experiment 1), and further, expanding on the research, whether perceptual biases would translate into the execution of a corresponding push pass action (Experiment 2). Based on predictions from the two-visual systems model, we hypothesized that the action-specific perceptual biases in distance perception would not translate into the control of movement. In Experiment 1, elite field hockey players estimated the distance from targets that differed in size before making push pass actions toward the target (i.e., the smaller targets being more difficult). Results showed that participants did estimate the perceived distance of the push pass task to be larger as a function of task difficulty. We found a similar result in Experiment 2, and in addition, manipulated the required outcome of the push-pass while measuring the speed of the push-pass and found that a perceptual bias did not translate into the execution of the actual push pass task (Experiment 2). In line with the action-specific account of perception, a perceptual bias arose that may assist in making adaptive action choices. However, consistent with the two-visual systems model, this perceptual bias did not affect subsequent control of movement, preventing it from becoming maladaptive. Implications for talent identification and development are briefly discussed

Fight without sight:The contribution of vision to judo performance

Objective: Although vision is typically considered the predominant sense for guiding performance, there are sports for which other senses are believed to be as important, if not more important than vision. Accordingly, in Paralympic judo, athletes with different degrees of vision impairment (VI) compete together based on the assumption that vision does not influence judo performance, as long as judokas start the match with their grip in place. The aim of this research was to test this assumption. Method: We conducted two studies. In the first we analysed data from two major recent VI judo competitions to compare the relative performance of blind and partially sighted athletes when competing against each other. In the second study, twenty-four able-sighted players competed in practice matches in sighted and blindfolded conditions. Results: In Study 1, we demonstrated that blind judokas win far less medals in VI judo competitions than their partially sighted opponents. In study 2, a significant performance advantage was found for sighted judokas fighting against blindfolded opponents. Conclusions: Vision enhances judo performance, even when judokas start the match with their grip in place. These findings suggest that it would be desirable to take measures to make VI judo competition fairer to those who are most severely impaired

Spatial shifts in swiping actions, the impact of "left" and "right" verbalizations

Movements are often modulated by the meaning of cue words. We explore the interaction between verbal and visual constraints during a movement by investigating if spoken words during movement execution bias late movement control of swiping actions on a tablet when vision of the target is removed during the movement. Verbalization trials required participants to vocalize the spatial directions 'LEFT', 'MIDDLE', or 'RIGHT' of the active target, relative to the other presented targets. A late influence of semantics emerged on movement execution in verbalized trials with action endpoints landing more in the direction of the spoken word than without verbalization. The emergence of the semantic effect as the movement progresses reflects the temporal unfolding of the visual and verbal constraints during the swiping action. Comparing our current results with a similar task using a variant verbalization, we also conclude that, larger semantic content effects are found with spatial direction than numerical magnitude verbalization

Nothing magical:pantomimed grasping is controlled by the ventral system

In a recent amendment to the two-visual-system model, it has been proposed that actions must result in tactile contact with the goal object for the dorsal system to become engaged (Whitwell et al., Neuropsychologia 55:41-50, 2014). The present study tested this addition by assessing the use of allocentric information in normal and pantomime actions. To this end, magicians, and participants who were inexperienced in performing pantomime actions made normal and pantomime grasps toward objects embedded in the Müller-Lyer illusion. During pantomime grasping, a grasp was made next to an object that was in full view (i.e., a displaced pantomime grasping task). The results showed that pantomime grasps took longer, were slower, and had smaller hand apertures than normal grasping. Most importantly, hand apertures were affected by the illusion during pantomime grasping but not in normal grasping, indicating that displaced pantomime grasping is based on allocentric information. This was true for participants without experience in performing pantomime grasps as well as for magicians with experience in pantomiming. The finding that the illusory bias is limited to pantomime grasping and persists with experience supports the conjecture that the normal engagement of the dorsal system's contribution requires tactile contact with a goal object. If no tactile contact is made, then movement control shifts toward the ventral system

Imperceptibly off-center goalkeepers influence penalty-kick direction in soccer

The penalty kick generates a variety of strong emotions in soccer (Carroll, Ebrahim, Tilling, Macleod, & Smith, 2002), and places the goalkeeper at such a disadvantage that only approximately 18% of penalty kicks are saved (Kropp & Trapp, 1999). We asked whether a goalkeeper can, by standing marginally left or right of goal center, bias a penalty taker implicitly to kick to the side with greater area, thus allowing the goalkeeper to dive in that direction to make a save. We show that the penalty taker is unlikely to be mindful that the goalkeeper is off center, but nevertheless can identify the side with greater area and will be more likely to direct the penalty kick to that side than to the other side