Cronan Glen E, Kuzminov Andrei
Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
bioRxiv. 2023 Nov 9:2023.11.08.566101. doi: 10.1101/2023.11.08.566101.
Protein degron tags have proven uniquely useful for characterization of gene function. Degrons mediate quick depletion, usually within minutes, of a protein of interest - allowing researchers to characterize cellular responses to the loss of function. To develop a general purpose degron tool in , we sought to build upon a previously characterized system of SspB-dependent inducible protein degradation. For this, we created a family of expression vectors containing a destabilized allele of SspB, capable of a rapid and nearly perfect "off-to-on" induction response. Using this system, we demonstrated control over several enzymes of DNA metabolism, but also found with other substates apparent limitations of a SspB-dependent system. Several degron target proteins were degraded too slowly to affect their complete depletion during active growth, whereas others appeared completely refractory to degron-promoted degradation. We demonstrated that a model substrate, beta-galactosidase, was positively recognized as a degron substrate, but failed to be degraded by the ClpXP protease - demonstrating an apparently unknown mechanism of protease resistance. Thus, only a minority of our, admittedly biased, selection of degron substates proved amenable to rapid SspB-catalyzed degradation. We conclude that substrate-dependence of the SspB system remains a critical factor for the success of this degron system. For substrates that prove degradable, we provide a series of titratable SspB-expression vehicles.
蛋白质降解标签已被证明在基因功能表征方面具有独特的用途。降解标签通常在几分钟内介导目标蛋白质的快速消耗,使研究人员能够表征细胞对功能丧失的反应。为了在[具体物种或系统]中开发一种通用的降解标签工具,我们试图在先前表征的依赖SspB的诱导型蛋白质降解系统的基础上进行构建。为此,我们创建了一系列表达载体,其中包含一个不稳定的SspB等位基因,能够实现快速且近乎完美的“关闭到开启”诱导反应。使用该系统,我们证明了对几种DNA代谢酶的控制,但也发现对于其他底物,依赖SspB的系统存在明显局限性。几种降解标签靶蛋白降解过慢,以至于在活跃生长期间无法实现完全消耗,而其他一些蛋白似乎对降解标签促进的降解完全无反应。我们证明,模型底物β-半乳糖苷酶被确认为降解标签底物,但不能被ClpXP蛋白酶降解,这表明存在一种明显未知的蛋白酶抗性机制。因此,在我们(诚然有偏向性)选择的降解标签底物中,只有少数被证明适合快速的SspB催化降解。我们得出结论,SspB系统的底物依赖性仍然是该降解标签系统成功的关键因素。对于可降解的底物,我们提供了一系列可滴定的SspB表达载体。