Structural evidence for non-canonical binding of Ca2+ to a canonical EF-hand of a conventional myosin
Structural evidence for non-canonical binding of Ca2+ to a canonical EF-hand of a conventional myosin
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DOI：
10.1074/jbc.m506315200
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发表时间：
2005-12-16
影响因子：
4.8
通讯作者：
Nyitray, L
中科院分区：
文献类型：
--
作者：
Debreczeni, JÉ;Farkas, L;Nyitray, L
我们以前已经确定了一个单一的抑制性钙离子结合位点的第一EF-手的绒泡菌常规肌球蛋白的基本轻链。作为一般规则，在钙调素家族的EF-手包含域的构象是“封闭”的情况下和“开放”的存在下，结合阳离子;一个值得注意的例外是不寻常的Ca 2+结合的封闭域中的Ca 2+激活的扇贝肌球蛋白的基本轻链。在这里，我们已经报道了1.8埃分辨率结构的调节域（RD）的绒泡菌肌球蛋白II，其中Ca 2+是绑定到一个典型的EF-手，也是在一个封闭的状态。EF-手环的第12位，通常在开放状态下为Ca 2+提供双齿配体，在结构中太远而不能参与离子的配位。该结构包括仅介导晶体接触的第二Ca 2+。为了揭示Ca 2+调节作用背后的机制，我们比较了配体和未配体RD的构象灵活性。我们的工作假设，即调节作用的Ca 2+对构象的灵活性的RD，是在与观察到的抑制氢氘交换率的Ca 2+结合的形式，以及与分子动力学计算的结果。基于这一证据，我们得出结论，Ca 2+诱导的RD结构动力学的变化是一个主要因素，在Ca 2+介导的调节绒泡菌肌球蛋白II活性。
We have previously identified a single inhibitory Ca2+-binding site in the first EF-hand of the essential light chain of Physarum conventional myosin. As a general rule, conformation of the EF-hand-containing domains in the calmodulin family is "closed" in the absence and "open" in the presence of bound cations; a notable exception is the unusual Ca2+-bound closed domain in the essential light chain of the Ca2+-activated scallop muscle myosin. Here we have reported the 1.8 angstrom resolution structure of the regulatory domain (RD) of Physarum myosin II in which Ca2+ is bound to a canonical EF- hand that is also in a closed state. The 12th position of the EF- hand loop, which normally provides a bidentate ligand for Ca2+ in the open state, is too far in the structure to participate in coordination of the ion. The structure includes a second Ca2+ that only mediates crystal contacts. To reveal the mechanism behind the regulatory effect of Ca2+, we compared conformational flexibilities of the liganded and unliganded RD. Our working hypothesis, i.e. the modulatory effect of Ca2+ on conformational flexibility of RD, is in line with the observed suppression of hydrogen-deuterium exchange rate in the Ca2+-bound form, as well as with results of molecular dynamics calculations. Based on this evidence, we concluded that Ca2+-induced change in structural dynamics of RD is a major factor in Ca2+-mediated regulation of Physarum myosin II activity.