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Imai S.,Fujitsu Limited | Leibnitz K.,Osaka University | Murata M.,Center for Information and Neural Networks t
IEICE Transactions on Information and Systems | Year: 2015

Content caching networks like Information-Centric Networking (ICN) are beneficial to reduce the network traffic by storing content data on routers near to users. In ICN, it becomes an important issue to manage system resources, such as storage and network bandwidth, which are influenced by cache characteristics of each cache node. Meanwhile, cache aging techniques based on Time-To-Live (TTL) of content facilitate analyzing cache characteristics and can realize appropriate resource management by setting efficient TTLs. However, it is difficult to search for the efficient TTLs in a distributed cache system connected by multiple cache nodes. Therefore, we propose an adaptive control mechanism of the TTL value of content in distributed cache systems by using predictive models which can estimate the impact of the TTL values on network resources and cache performance. Furthermore, we show the effectiveness of the proposed mechanism. Copyright © 2015 The Institute of Electronics, Information and Communication Engineers. Source

Karagiannis P.,RIKEN | Ishii Y.,Osaka University | Yanagida T.,RIKEN | Yanagida T.,Osaka University | Yanagida T.,Center for Information and Neural Networks t
Chemical Reviews | Year: 2014

Myosin movement depends on the hand-over-hand mechanism, which involves a reliable set of ordered movements in the myosin structure. Myosin II assembles to form muscle, making it the rare molecular motor that can be studied at the macroscopic level. When ATP binds to myosin, it causes the latter to dissociate from the actin filament and take the detached state. As ATP is hydrolyzed, the myosin conformation changes to bind to the actin filament weakly. This step is followed by one that generates forces and leads to the release of the hydrolysis products, Pi and ADP, in that order. The Brownian component of the stepping mechanism is particularly important in myosin VI, because this myosin can act both as a transporter and as an anchor, with the function depending on the external force. At higher forces, transportation is very inefficient, and myosin VI shows more frequent anchoring tendencies. While myosin moves forward using a combination of a power stroke and Brownian search, single molecule studies have revealed that it can at times also move backward, especially at high forces. Source

Ikezaki K.,Osaka University | Komori T.,Osaka University | Sugawa M.,Osaka University | Arai Y.,Osaka University | And 5 more authors.
Small | Year: 2012

Myosin VI is an adenosine triphosphate (ATP)-driven dimeric molecular motor that has dual function as a vesicle transporter and a cytoskeletal anchor. Recently, it was reported that myosin VI generates three types of steps by taking either a distant binding or adjacent binding state (noncanonical hand-over-hand step pathway). The adjacent binding state, in which both heads bind to an actin filament near one another, is unique to myosin VI and therefore may help explain its distinct features. However, detailed information of the adjacent binding state remains unclear. Here simultaneous observations of the head and tail domain during stepping are presented. These observations show that the lever arms tilt forward in the adjacent binding state. Furthermore, it is revealed that either head could take the subsequent step with equal probability from this state. Together with previous results, a comprehensive stepping scheme is proposed; it includes the tail domain motion to explain how myosin VI achieves its dual function. Myosin VI steps are highly constrained by the forward tilt of the lever arm domains, as this tilt allows a single backward step from the distant binding state, prohibiting backward step generation from the adjacent binding state. Such constraints are important for achieving myosin VI's dual function. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Ikezaki K.,Osaka University | Ikezaki K.,RIKEN | Komori T.,Osaka University | Arai Y.,Osaka University | And 3 more authors.
Biophysics (Japan) | Year: 2015

Myosin VI is a processive myosin that has a unique stepping motion, which includes three kinds of steps: a large forward step, a small forward step and a backward step. Recently, we proposed the parallel lever arms model to explain the adjacent binding state, which is necessary for the unique motion. In this model, both lever arms are directed the same direction. However, experimental evidence has not refuted the possibility that the adjacent binding state emerges from myosin VI folding its lever arm extension (LAE). To clarify this issue, we constructed a myosin VI/V chimera that replaces the myosin VI LAE with the IQ3-6 domains of the myosin V lever arm, which cannot fold, and performed single molecule imaging. Our chimera showed the same stepping patterns as myosin VI, indicating the LAE is not responsible for the adjacent binding state. © 2015 The biophysical society of Japan. Source

Ikezaki K.,Osaka University | Ikezaki K.,RIKEN | Komori T.,Osaka University | Komori T.,RIKEN | And 3 more authors.
PLoS ONE | Year: 2013

Myosin VI is an ATP driven molecular motor that normally takes forward and processive steps on actin filaments, but also on occasion stochastic backward steps. While a number of models have attempted to explain the backwards steps, none offer an acceptable mechanism for their existence. We therefore performed single molecule imaging of myosin VI and calculated the stepping rates of forward and backward steps at the single molecule level. The forward stepping rate was proportional to the ATP concentration, whereas the backward stepping rate was independent. Using these data, we proposed that spontaneous detachment of the leading head is uncoupled from ATP binding and is responsible for the backward steps of myosin VI. © 2013 Ikezaki et al. Source

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