Zhang Susan, Burns-Huang Kristin E, Janssen Guido V, Li Huilin, Ovaa Huib, Hedstrom Lizbeth, Darwin K Heran
Department of Microbiology, New York University School of Medicine, New York, New York, USA.
Department of Chemical Immunology, Leiden University Medical Center, Leiden, The Netherlands.
mBio. 2017 Feb 21;8(1):e00122-17. doi: 10.1128/mBio.00122-17.
The protein degradation machinery of includes a proteasome and a ubiquitin-like protein (Pup). Proteasome accessory factor A (PafA) attaches Pup to proteins to target them for degradation by the proteasome. Free Pup is unstable and never observed in extracts of , an observation that led us to hypothesize that PafA may need alternative sources of Pup. Here, we show that PafA can move Pup from one proteasome substrate, inositol 1-phosphate synthetase (Ino1), to two different proteins, malonyl coenzyme A (CoA)-acyl carrier protein transacylase (FabD) and lonely guy (Log). This apparent "transpupylation" reaction required a previously unrecognized depupylase activity in PafA, and, surprisingly, this depupylase activity was much more efficient than the activity of the dedicated depupylase Dop (deamidase of Pup). Thus, PafA can potentially use both newly synthesized Pup and recycled Pup to doom proteins for degradation. Unlike eukaryotes, which contain hundreds of ubiquitin ligases, Pup-containing bacteria appear to have a single ligase to pupylate dozens if not hundreds of different proteins. The observation that PafA can depupylate and transpupylate offers new insight into how protein stability is regulated in proteasome-bearing bacteria. Importantly, PafA and the dedicated depupylase Dop are each required for the full virulence of Thus, inhibition of both enzymes may be extremely attractive for the development of therapeutics against tuberculosis.
[细菌名称]的蛋白质降解机制包括一个蛋白酶体和一种类泛素蛋白（Pup）。蛋白酶体辅助因子A（PafA）将Pup附着到蛋白质上，使其成为蛋白酶体降解的目标。游离的Pup不稳定，在[细菌名称]的提取物中从未观察到，这一观察结果使我们推测PafA可能需要Pup的其他来源。在这里，我们表明PafA可以将Pup从一种蛋白酶体底物，即肌醇1-磷酸合成酶（Ino1），转移到两种不同的蛋白质，丙二酰辅酶A（CoA）-酰基载体蛋白转酰基酶（FabD）和孤独者（Log）上。这种明显的“转Pup化”反应需要PafA中一种先前未被认识的去Pup化酶活性，而且令人惊讶的是，这种去Pup化酶活性比专门的去Pup化酶Dop（Pup脱氨酶）的活性要高效得多。因此，PafA可能既能利用新合成的Pup，也能利用循环利用的Pup来使蛋白质注定被降解。与含有数百种泛素连接酶的真核生物不同，含Pup的细菌似乎只有一种连接酶来将Pup连接到数十种甚至数百种不同的蛋白质上。PafA可以去除Pup并进行转Pup化的这一观察结果，为含有蛋白酶体的细菌中蛋白质稳定性是如何被调控提供了新的见解。重要的是，PafA和专门的去Pup化酶Dop都是[细菌名称]完全毒力所必需的。因此，抑制这两种酶对于开发抗结核病治疗药物可能极具吸引力。
