Department of Biochemistry, University of Washington, Seattle, WA, USA.
Department of Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT, USA.
Nat Commun. 2024 Feb 28;15(1):1840. doi: 10.1038/s41467-024-46111-3.
The cytoskeletal protein actin plays a critical role in the pathogenicity of the intracellular parasite, Toxoplasma gondii, mediating invasion and egress, cargo transport, and organelle inheritance. Advances in live cell imaging have revealed extensive filamentous actin networks in the Apicomplexan parasite, but there are conflicting data regarding the biochemical and biophysical properties of Toxoplasma actin. Here, we imaged the in vitro assembly of individual Toxoplasma actin filaments in real time, showing that native, unstabilized filaments grow tens of microns in length. Unlike skeletal muscle actin, Toxoplasma filaments intrinsically undergo rapid treadmilling due to a high critical concentration, fast monomer dissociation, and rapid nucleotide exchange. Cryo-EM structures of jasplakinolide-stabilized and native (i.e. unstabilized) filaments show an architecture like skeletal actin, with differences in assembly contacts in the D-loop that explain the dynamic nature of the filament, likely a conserved feature of Apicomplexan actin. This work demonstrates that evolutionary changes at assembly interfaces can tune the dynamic properties of actin filaments without disrupting their conserved structure.
细胞骨架蛋白肌动蛋白在细胞内寄生虫弓形虫的致病性中起着关键作用，介导入侵和出芽、货物运输和细胞器遗传。活细胞成像的进展揭示了顶复门寄生虫中广泛的丝状肌动蛋白网络，但关于弓形虫肌动蛋白的生化和生物物理特性存在相互矛盾的数据。在这里，我们实时成像了单个弓形虫肌动蛋白丝的体外组装，显示出天然的、未稳定的丝状体可生长数十微米。与骨骼肌肌动蛋白不同，由于临界浓度高、单体解离快和核苷酸交换快，弓形虫丝状体内在地经历快速的 treadmilling。漆酶稳定和天然（即未稳定）丝状体的冷冻电镜结构显示出类似于骨骼肌肌动蛋白的结构，在 D 环中的组装接触存在差异，这解释了丝状体的动态性质，可能是 Apicomplexan 肌动蛋白的一个保守特征。这项工作表明，在组装界面的进化变化可以调节肌动蛋白丝的动态特性，而不会破坏其保守结构。
