tailieunhanh - Báo cáo khoa học: Motion of the Ca2+ -pump captured

Studies of ion pumps, such as ATP synthetase and Ca 2+ -ATPase, have a long history. The crystal structures of several kinds of ion pump have been resolved, and provide static pictures of mechanisms of ion transport. | IFEBS Journal Motion of the Ca2 -pump captured Masatoshi Yokokawa1 2 and Kunio Takeyasu1 1 Kyoto University Graduate Schoolof Biostudies Japan 2 Graduate Schoolof Pure and Applied Science University of Tsukuba Japan Keywords atomic force microscopy ion pump P-type ATPase SERCA single molecular reaction analysis Correspondence M. Yokokawa Graduate Schoolof Pure and Applied Science University of Tsukuba 1-1-1 Tennoudai Tsukuba 305-8573 Japan Fax 81 29 853 4490 Tel 81 29 853 5600 5466 E-mail yokokawa@ Received 9 March 2011 revised 24 May 2011 accepted 16 June 2011 doi Studies of ion pumps such as ATP synthetase and Ca2 -ATPase have a long history. The crystal structures of several kinds of ion pump have been resolved and provide static pictures of mechanisms of ion transport. In this study using fast-scanning atomic force microscopy we have visualized conformational changes in the sarcoplasmic reticulum Ca2 -ATPase SERCA in real time at the single-molecule level. The analyses of individual SERCA molecules in the presence of both ATP and free Ca2 revealed up-down structural changes corresponding to the Albers-Post scheme. This fluctuation was strongly affected by the ATP and Ca2 concentrations and was prevented by an inhibitor thapsigargin. Interestingly at a physiological ATP concentrations the up-down motion disappeared completely. These results indicate that SERCA does not transit through the shortest structure and has a catalytic pathway different from the ordinary Albers-Post scheme under physiological conditions. Introduction Skeletal muscle contraction is subject to actin-linked regulation by troponins 1 2 . The physiological player in its molecular mechanism is Ca2 which is released into the cytoplasm from the sarcoplasmic reticulum SR through the Ca2 -release channel. This removes the troponin inhibition of the actin-myosin interaction and induces muscle contraction. When the muscle relaxes Ca2 needs to be .

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