Ferguson C, Lakey A, Hutchings A, Butcher G W, Leonard K R, Bullard B
European Molecular Biology Laboratory, Heidelberg, Germany.
J Cell Sci. 1994 May;107 ( Pt 5):1115-29. doi: 10.1242/jcs.107.5.1115.
Asynchronous insect flight muscles produce oscillatory contractions and can contract at high frequency because they are activated by stretch as well as by Ca2+. Stretch activation depends on the high stiffness of the fibres and the regular structure of the filament lattice. Cytoskeletal proteins may be important in stabilising the lattice. Two proteins, zeelin 1 (35 kDa) and zeelin 2 (23 kDa), have been isolated from the cytoskeletal fraction of Lethocerus flight muscle. Both zeelins have multiple isoforms of the same molecular mass and different charge. Zeelin 1 forms micelles and zeelin 2 forms filaments when renatured in low ionic strength solutions. Filaments of zeelin 2 are ribbons 10 nm wide and 3 nm thick. The position of zeelins in fibres from Lethocerus flight and leg muscle was determined by immunofluorescence and immunoelectron microscopy. Zeelin 1 is found in flight and leg fibres and zeelin 2 only in flight fibres. In flight myofibrils, both zeelins are in discrete regions of the A-band in each half sarcomere. Zeelin 1 is across the whole A-band in leg myofibrils. Zeelins are not in the Z-disc, as was thought previously, but migrate to the Z-disc in glycerinated fibres. Zeelins are associated with thick filaments and analysis of oblique sections showed that zeelin 1 is closer to the filament shaft than zeelin 2. The antibody labelling pattern is consistent with zeelin molecules associated with myosin near the end of the rod region. Alternatively, the position of zeelins may be determined by other A-band proteins. There are about 2.0 to 2.5 moles of myosin per mole of each zeelin. The function of these cytoskeletal proteins may be to maintain the ordered structure of the thick filament.
异步昆虫飞行肌产生振荡收缩，并且能够高频收缩，因为它们不仅由Ca2+激活，还受拉伸激活。拉伸激活取决于纤维的高刚度和细丝晶格的规则结构。细胞骨架蛋白可能在稳定晶格方面很重要。从田鳖飞行肌的细胞骨架部分分离出了两种蛋白质，zeelin 1（35 kDa）和zeelin 2（23 kDa）。两种zeelin都有相同分子量但电荷不同的多种异构体。当在低离子强度溶液中复性时，zeelin 1形成微团，zeelin 2形成细丝。zeelin 2的细丝是宽10 nm、厚3 nm的带状物。通过免疫荧光和免疫电子显微镜确定了zeelin在田鳖飞行肌和腿部肌肉纤维中的位置。在飞行肌纤维和腿部纤维中都发现了zeelin 1，而zeelin 2仅存在于飞行肌纤维中。在飞行肌原纤维中，两种zeelin都位于每个半肌节A带的离散区域。在腿部肌原纤维中，zeelin 1横跨整个A带。zeelin并不像之前认为的那样位于Z盘，而是在甘油处理的纤维中迁移到Z盘。zeelin与粗丝相关，对斜截面的分析表明zeelin 1比zeelin 2更靠近丝轴。抗体标记模式与zeelin分子在杆状区域末端附近与肌球蛋白相关一致。或者，zeelin的位置可能由其他A带蛋白决定。每摩尔每种zeelin约有2.0至2.5摩尔的肌球蛋白。这些细胞骨架蛋白的功能可能是维持粗丝的有序结构。
