Castaing Jean-Philippe, Lee Scarlett, Anantharaman Vivek, Ravilious Geoffrey E, Aravind L, Ramamurthi Kumaran S
Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
FEMS Microbiol Lett. 2014 Sep;358(2):145-53. doi: 10.1111/1574-6968.12452. Epub 2014 May 20.
Spores of Bacillus subtilis are dormant cell types that are formed when the bacterium encounters starvation conditions. Spores are encased in a shell, termed the coat, which is composed of approximately seventy different proteins and protects the spore's genetic material from environmental insults. The structural component of the basement layer of the coat is an exceptional cytoskeletal protein, termed SpoIVA, which binds and hydrolyzes ATP. ATP hydrolysis is utilized to drive a conformational change in SpoIVA that leads to its irreversible self-assembly into a static polymer in vitro. Here, we characterize the middle domain of SpoIVA, the predicted secondary structure of which resembles the chemotaxis protein CheX but, unlike CheX, does not harbor residues required for phosphatase activity. Disruptions in this domain did not abolish ATP hydrolysis, but resulted in mislocalization of the protein and reduction in sporulation efficiency in vivo. In vitro, disruptions in this domain prevented the ATP hydrolysis-driven conformational change in SpoIVA required for polymerization and led to the aggregation of SpoIVA into particles that did not form filaments. We propose a model in which SpoIVA initially assumes a conformation in which it inhibits its own aggregation into particles, and that ATP hydrolysis remodels the protein so that it assumes a polymerization-competent conformation.
枯草芽孢杆菌的孢子是一种休眠细胞类型，当细菌遇到饥饿条件时形成。孢子被包裹在一层称为外壳的结构中，外壳由大约70种不同的蛋白质组成，可保护孢子的遗传物质免受环境损伤。外壳底层的结构成分是一种特殊的细胞骨架蛋白，称为SpoIVA，它能结合并水解ATP。ATP水解被用于驱动SpoIVA的构象变化，使其在体外不可逆地自组装成一种静态聚合物。在此，我们对SpoIVA的中间结构域进行了表征，其预测的二级结构类似于趋化蛋白CheX，但与CheX不同的是，它不含有磷酸酶活性所需的残基。该结构域的破坏并没有消除ATP水解，但导致了该蛋白的定位错误，并降低了体内的孢子形成效率。在体外，该结构域的破坏阻止了SpoIVA聚合所需的由ATP水解驱动的构象变化，并导致SpoIVA聚集成不形成细丝的颗粒。我们提出了一个模型，其中SpoIVA最初呈现一种构象，在这种构象中它抑制自身聚集成颗粒，而ATP水解重塑该蛋白，使其呈现一种具备聚合能力的构象。
