Department of Biology, Brandeis University, 415 South Street, Waltham, MA 02454, USA.
Department of Biochemistry, Brandeis University, 415 South Street, Waltham, MA 02454, USA.
Curr Biol. 2023 Oct 23;33(20):4484-4495.e5. doi: 10.1016/j.cub.2023.09.032. Epub 2023 Oct 4.
How actin filaments are spatially organized and remodeled into diverse higher-order networks in vivo is still not well understood. Here, we report an unexpected F-actin "coalescence" activity driven by cyclase-associated protein (CAP) and enhanced by its interactions with actin-binding protein 1 (Abp1). We directly observe S. cerevisiae CAP and Abp1 rapidly transforming branched or linear actin networks by bundling and sliding filaments past each other, maximizing filament overlap, and promoting compaction into bundles. This activity does not require ATP and is conserved, as similar behaviors are observed for the mammalian homologs of CAP and Abp1. Coalescence depends on the CAP oligomerization domain but not the helical folded domain (HFD) that mediates its functions in F-actin severing and depolymerization. Coalescence by CAP-Abp1 further depends on interactions between CAP and Abp1 and interactions between Abp1 and F-actin. Our results are consistent with a mechanism in which the formation of energetically favorable sliding CAP and CAP-Abp1 crosslinks drives F-actin bundle compaction. Roles for CAP and CAP-Abp1 in actin remodeling in vivo are supported by strong phenotypes arising from deletion of the CAP oligomerization domain and by genetic interactions between sac6Δ and an srv2-301 mutant that does not bind Abp1. Together, these observations identify a new actin filament remodeling function for CAP, which is further enhanced by its direct interactions with Abp1.
肌动蛋白丝在体内是如何进行空间组织并重塑成不同的高级网络的，目前仍不清楚。在这里，我们报告了一种意想不到的肌动蛋白丝“聚合”活性，它由环化酶相关蛋白（CAP）驱动，并通过其与肌动蛋白结合蛋白 1（Abp1）的相互作用得到增强。我们直接观察到酿酒酵母 CAP 和 Abp1 通过捆绑和滑动纤维相互穿过，最大限度地增加纤维重叠，并促进纤维紧凑成束，从而快速将分支或线性肌动蛋白网络转化。这种活性不需要 ATP，并且是保守的，因为 CAP 和 Abp1 的哺乳动物同源物也表现出类似的行为。聚合依赖于 CAP 的寡聚化结构域，但不依赖于介导其在 F-肌动蛋白切割和解聚中的功能的螺旋折叠结构域（HFD）。CAP-Abp1 的聚合进一步依赖于 CAP 和 Abp1 之间的相互作用以及 Abp1 和 F-肌动蛋白之间的相互作用。我们的结果与一种机制一致，即形成有利能量的滑动 CAP 和 CAP-Abp1 交联驱动 F-肌动蛋白束的紧密化。CAP 在体内肌动蛋白重塑中的作用得到了 sac6Δ 缺失和不结合 Abp1 的 srv2-301 突变体之间遗传相互作用的强烈表型的支持。总之，这些观察结果确定了 CAP 的一种新的肌动蛋白丝重塑功能，它通过与 Abp1 的直接相互作用得到进一步增强。
