Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut, USA.
J Bacteriol. 2012 May;194(9):2205-13. doi: 10.1128/JB.00039-12. Epub 2012 Mar 2.
Bacterial SecA proteins can be categorized by the presence or absence of a variable subdomain (VAR) located within nucleotide-binding domain II of the SecA DEAD motor. Here we show that VAR is dispensable for SecA function, since the VAR deletion mutant secAΔ519-547 displayed a wild-type rate of cellular growth and protein export. Loss or gain of VAR is extremely rare in the history of bacterial evolution, indicating that it appears to contribute to secA function within the relevant species in their natural environments. VAR removal also results in additional secA phenotypes: azide resistance (Azi(r)) and suppression of signal sequence defects (PrlD). The SecAΔ(519-547) protein was found to be modestly hyperactive for SecA ATPase activities and displayed an accelerated rate of ADP release, consistent with the biochemical basis of azide resistance. Based on our findings, we discuss models whereby VAR allosterically regulates SecA DEAD motor function at SecYEG.
细菌 SecA 蛋白可以根据核苷酸结合域 II 中存在或不存在可变亚域（VAR）来分类。在这里，我们表明 VAR 对于 SecA 功能是可有可无的，因为 VAR 缺失突变体 secAΔ519-547 显示出与野生型相当的细胞生长和蛋白输出速率。VAR 的缺失或获得在细菌进化的历史上极为罕见，这表明它似乎有助于 VAR 在相关物种的自然环境中发挥 secA 功能。VAR 的去除也会导致其他 secA 表型：叠氮抗性（Azi(r)）和信号序列缺陷（PrlD）的抑制。发现 SecAΔ(519-547)蛋白对 SecA ATP 酶活性具有适度的超活性，并显示出 ADP 释放的加速速率，这与叠氮抗性的生化基础一致。基于我们的发现，我们讨论了 VAR 以变构方式调节 SecA DEAD 马达在 SecYEG 上的功能的模型。
