HCM is characterized by thickening of the left ventricular wall and the interventricular septum, and abnormality is suspected in contractile functions. Here, we studied the role of a human α-tropomyosin (Tm) mutant V95A in Ca2+ regulation of contraction. Thin filaments reconstituted with actin, troponin and Tm V95A were examined in in vitro motility assays, where the sliding velocity was measured between R.T. and 40℃ and the sliding force with optical tweezers at R.T. We found that the thermal

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... ensitivity of thin filaments reconstituted with V95A decreased compared to WT. This can be attributed to the lower binding affinity of V95A to actin, which may initiate maladaptive HCM. Similar results have been obtained in D175N, which is also known to cause HCM in humans. 1P140 ミオシンフィラメント懸濁液の ATP 存在下でのプロトン NMR 緩和経過 Spin-spin relaxation of 1H NMR signals from myosin filaments suspension with or without ATP The dynamic changes of water molecules structure surrounding contractile proteins might play an important role in cross-bridge cycling during contraction. The spin-spin relaxation process of 1H-NMR signals from suspension of myosin filaments prepared from rabbit could be well represented by the summation of several exponentials indicating that water molecules in the suspension could be conveniently grouped into several components based on the relaxation time constant (T2). The slowest two components (T2 around 0.4s and 0.15s) dominated over faster relaxation components. This may suggest that the potential of the water molecules existing around myosin filaments is high. F-actin plays important roles in various cellular activities through interaction with actin binding proteins (ABPs). The ABPs specify function and intracellular localization of F-actin. However, how each ABP recognizes specific actin filaments within a cell is largely unknown. Here, we identified ABPs whose actin binding domains (ABDs) can localize at specific actin filaments within Dictyostelium cells when expressed as GFPfusions. Since the ABDs are not expected to interact with any molecules except F-actin, they probably distinguish the structural difference of Factin. Our findings suggest that the interaction between F-actin and an ABP cooperatively changes the F-actin structure, increasing or decreasing the affinity of the F-actin for various ABPs. 1P142 昆虫飛翔筋線維の収縮蛋白交換実験と X 線回折 X-ray diffraction from insect flight muscle with exchanged contractile proteins Hiroyuki Iwamoto, Naoto Yagi (SPring-8 JASRI) The function of stretch activation is essential for the asynchronous action of insect flight muscle (IFM), and the molecular mechanism for sensing of mechanical stretch has been unknown. We have shown evidence that the stretch-sensing mechanism is built into myosin heads themselves, and have proposed a mechanism in which pre-force attached myosin heads are converted to a force producing form when they are distorted in a specific manner by stretch. To further test this proposal, we are currently trying to exchange contractile proteins of IFM fibers with those from different sources, such as vertebrate skeletal muscle. Fluorescently labeled rabbit myosin is incorporated into IFM fibers, and X-ray diffraction patterns indicate the presence of myosin filaments. 1P143 タキソールは、急速な微小管内チューブリン周期の伸長を誘 導する Microtubules (MT) are key components of the cytoskeleton in eukaryotic cells. One of the most fundamental questions is how MT dynamics is associated with the molecular conformation of tubulin dimers within MTs. To address the issues, we applied our new technique for the rapid shearflow alignment of biological filaments, which enabled us to acquire X-ray fiber diffraction data in seconds from native MTs under various physiological conditions. We found that the longitudinal repeat of tubulin dimers in MTs were elongated from 3.88 to 4.03 nm within 1 min after adding paclitaxel. Diameter changes appeared to be occurring in a slow time course (10-20 min). It is suggested paclitaxel induces quick elongation of tubulin dimers in MTs. 1P144 V1-ATPase の粗視化分子動力学シミュレーション Course-grained molecular dynamics simulation of V1-ATPase Hiroki Kashimura, Yuta Isaka, Yuichi Kokabu, Mitsunori Ikeguchi (Yokohama City Univ.) V-ATPase is a molecular motor acting as ion pump. The soluble domain of V-ATPase (V1) is composed of the central stalk (DF) and hexamer ring (A3B3): three catalytic A-subunits and three B-subunits are alternatively arranged around DF. Coupled with an ATP hydrolysis, conformational changes of A3B3 induce a 120-degree rotation of DF. To elucidate the relationship between the conformational changes and the rotation, we conducted a coarse-grained MD simulation using Go-model. By switching Go-potentials of A3B3, we forced to change the A3B3 structure, and prepared two states before and after the 120-degree rotation of DF. We then analyzed the dynamics of DF in response to the conformational changes of A3B3.