Plants utilize multiple isoforms of villin, an F-actin regulating protein with an N-terminal gelsolin-like core and a distinct C-terminal headpiece domain. Unlike their vertebrate homologues, plant villins have a much longer linker polypeptide connecting the core and headpiece. Moreover, the linker–headpiece connection region in plant villins lacks sequence homology to the vertebrate villin sequences. It is unknown to what extent the plant villin headpiece structure and function resemble those of the well-studied vertebrate counterparts. Here we present the first solution NMR structure and backbone dynamics characterization of a headpiece from plants, villin isoform 4 from Arabidopsis thaliana. The villin 4 headpiece is a 63-residue domain (V4HP63) that adopts a typical headpiece fold with an aromatics core and a tryptophan-centered hydrophobic cap within its C-terminal subdomain. However, V4HP63 has a distinct N-terminal subdomain fold as well as a novel, high mobility loop due to the insertion of serine residue in the canonical sequence that follows the variable length loop in headpiece sequences. The domain binds actin filaments with micromolar affinity, like the vertebrate analogues. However, the V4HP63 surface charge pattern is novel and lacks certain features previously thought necessary for high-affinity F-actin binding. Utilizing the updated criteria for strong F-actin binding, we predict that the headpiece domains of all other villin isoforms in A. thaliana have high affinity for F-actin.

中文翻译：

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植物维林头饰域展示了F-肌动蛋白的新型表面电荷模式和高亲和力

植物利用了villin的多种同工型，villin是一种F-肌动蛋白调节蛋白，具有N端凝溶胶蛋白样核心和独特的C端头域。与它们的脊椎动物同源物不同，植物维林具有更长的连接多肽，其连接核心和头部。此外，植物维林中的接头-头部连接区域缺乏与脊椎动物维林序列的序列同源性。尚不知道植物villin头件的结构和功能在多大程度上类似于经过充分研究的脊椎动物对应物。在这里，我们介绍了植物的头部，拟南芥的villin亚型4的第一个溶液NMR结构和主链动力学表征。villin 4头饰是一个63个残基的域（V4HP63），采用典型的头饰折叠，在其C末端亚域内具有芳香族核心和色氨酸中心的疏水性帽。但是，V4HP63具有独特的N末端亚结构域折叠以及新颖的高迁移率环，这是由于在头部序列中可变长度环之后的规范序列中插入了丝氨酸残基。该结构域以微摩尔亲和力结合肌动蛋白丝，如脊椎动物类似物。但是，V4HP63表面电荷图谱是新颖的，并且缺少以前认为对于高亲和力F-肌动蛋白结合所必需的某些特征。利用强大的F-肌动蛋白结合的更新的标准，我们预测拟南芥中所有其他villin同工型的头域对F-肌动蛋白具有高亲和力。