Atomic view into Plasmodium actin polymerization, ATP hydrolysis, and fragmentation
Atomic view into Plasmodium actin polymerization, ATP hydrolysis, and fragmentation
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DOI：
10.1371/journal.pbio.3000315
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发表时间：
2019-06-01
期刊：
影响因子：
9.8
通讯作者：
Kursula, Inari
中科院分区：
文献类型：
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作者：
Kumpula, Esa-Pekka;Lopez, Andrea J.;Kursula, Inari
疟原虫肌动蛋白形成非常短的细丝，并且在ATP水解和聚合之间具有非典型的联系。长丝是有害的寄生虫，但限制疟原虫微丝长度的结构因素仍然未知。使用高分辨率晶体学，我们表明，镁结合导致疟原虫肌动蛋白I单体的轻微扁平化，随后的磷酸盐释放导致更扭曲的构象。因此，Mg结合的单体在构象上比Ca形式更接近丝状（F）肌动蛋白，并且这可能促进聚合。一个协调的钾离子在水解过程中驻留在活性位点，并与磷酸盐一起离开，这是一个由含有Arg 178/Asp 180的A环的位置决定的过程。Asp 180与Lys 270或His 74相互作用，这取决于组氨酸的质子化状态，而Arg 178连接肌动蛋白原聚体的内部和外部结构域（ID和OD）。因此，A环充当稳定和不稳定细丝构象之间的开关，后者导致片段化。我们的数据提供了一个全面的模型聚合，ATP水解和磷酸盐的释放，和分裂的寄生虫微丝。类似的机制可能也存在于典型肌动蛋白中，尽管由于几个细微的序列差异以及His 73的甲基化（在疟原虫肌动蛋白I中相应的His 74上不存在），片段化不太有利。
Plasmodium actins form very short filaments and have a noncanonical link between ATP hydrolysis and polymerization. Long filaments are detrimental to the parasites, but the structural factors constraining Plasmodium microfilament lengths have remained unknown. Using high-resolution crystallography, we show that magnesium binding causes a slight flattening of the Plasmodium actin I monomer, and subsequent phosphate release results in a more twisted conformation. Thus, the Mg-bound monomer is closer in conformation to filamentous (F) actin than the Ca form, and this likely facilitates polymerization. A coordinated potassium ion resides in the active site during hydrolysis and leaves together with the phosphate, a process governed by the position of the Arg178/Asp180-containing A loop. Asp180 interacts with either Lys270 or His74, depending on the protonation state of the histidine, while Arg178 links the inner and outer domains (ID and OD) of the actin protomer. Hence, the A loop acts as a switch between stable and unstable filament conformations, the latter leading to fragmentation. Our data provide a comprehensive model for polymerization, ATP hydrolysis and phosphate release, and fragmentation of parasite microfilaments. Similar mechanisms may well exist in canonical actins, although fragmentation is much less favorable due to several subtle sequence differences as well as the methylation of His73, which is absent on the corresponding His74 in Plasmodium actin I.