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首页> 外文期刊>Journal of Molecular Biology >The structure of the FnIII Tandem A77-A78 points to a periodically conserved architecture in the myosin-binding region of titin.
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The structure of the FnIII Tandem A77-A78 points to a periodically conserved architecture in the myosin-binding region of titin.

机译：FnIII串联A77-A78的结构指向了肌蛋白肌球蛋白结合区中的周期性保守结构。

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摘要

Titin is a large intrasarcomeric protein that, among its many roles in muscle, is thought to modulate the in vivo assembly of the myosin motor filament. This is achieved through the molecular template properties of its A-band region, which is composed of fibronectin type III (FnIII) and immunoglobulin (Ig) domains organized into characteristic 7-domain (D-zone) and 11-domain (C-zone) superrepeats. Currently, there is little knowledge on the structural details of this region of titin. Here we report the conformational characterization of three FnIII tandems, A77-A78, A80-A82, and A84-A86, which are components of the representative fourth C-zone superrepeat. The structure of A77-A78 has been elucidated by X-ray crystallography to 1.65 A resolution, while low-resolution models of A80-A82 and A84-A86 have been calculated using small-angle X-ray scattering. A77-A78 adopts an extended "up-down" domain arrangement, where domains are connected by a hydrophilic three-residue linker sequence. The linker is embedded in a rich network of polar contacts at the domain interface that results in a stiff molecular conformation. The models of A80-A82 and A84-A86, which contain hydrophobic six-residue-long interdomain linkers, equally showed elongated molecular shapes, but with slightly coiled or zigzagged conformations. Small-angle X-ray scattering data further suggested that the long linkers do not result in a noticeable increase in molecular flexibility but lead to semibent domain arrangements. Our findings indicate that the structural characteristics of FnIII tandems from A-band titin contrast markedly with those of poly-Ig tandems from the elastic I-band, which exhibit domain interfaces depleted of interactions and compliant conformations. Furthermore, the analysis of sequence conservation in FnIII domains from A-band titin points to the existence of conformationally defined interfaces at specific superrepeat positions, possibly leading to a periodic and locally ordered architecture supporting the molecular scaffold properties of this region of titin.
机译：Titin是一种大的肌节内蛋白，在肌肉中有许多作用，据认为可调节肌球蛋白运动丝的体内组装。这是通过其A带区域的分子模板特性来实现的，该区域由III型纤连蛋白（FnIII）和免疫球蛋白（Ig）结构域组成，组织为7区（D区）和11区（C区） ）超级重复。目前，关于此蛋白区域的结构细节知之甚少。在这里，我们报告三个FnIII tandems（A77-A78，A80-A82和A84-A86）的构象表征，它们是代表性的第四C区超重复序列的组成部分。 X射线晶体学已阐明A77-A78的结构为1.65 A分辨率，而A80-A82和A84-A86的低分辨率模型已使用小角度X射线散射进行了计算。 A77-A78采用扩展的“上-下”结构域排列，其中结构域通过亲水性三残基接头序列连接。接头在结构域界面处嵌入丰富的极性接触网络中，从而导致分子构象变硬。包含疏水性六残基长的域间连接子的A80-A82和A84-A86模型同样显示出细长的分子形状，但具有轻微的盘绕或Z字形构象。小角度X射线散射数据进一步表明，长连接子不会导致分子柔性显着增加，但会导致半弯曲的域排列。我们的研究结果表明，来自A波段钛的FnIII坦丹的结构特征与来自弹性I波段的聚Ig坦丹的结构特征形成鲜明对比，后者显示出缺乏相互作用和顺应性构象的域界面。此外，从A带titin的FnIII域中的序列保守性分析表明，在特定的超级重复位置存在构象定义的界面，这可能导致支持titin区域分子支架特性的周期性和局部有序的体系结构。

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