Interdisciplinary Biological Sciences Graduate Program, Northwestern University, Evanston, IL, United States.
Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL, United States.
J Mol Biol. 2021 Jan 22;433(2):166721. doi: 10.1016/j.jmb.2020.11.020. Epub 2020 Nov 21.
Protein self-assembly is a common and essential biological phenomenon, and bacterial microcompartments present a promising model system to study this process. Bacterial microcompartments are large, protein-based organelles which natively carry out processes important for carbon fixation in cyanobacteria and the survival of enteric bacteria. These structures are increasingly popular with biological engineers due to their potential utility as nanobioreactors or drug delivery vehicles. However, the limited understanding of the assembly mechanism of these bacterial microcompartments hinders efforts to repurpose them for non-native functions. Here, we comprehensively investigate proteins involved in the assembly of the 1,2-propanediol utilization bacterial microcompartment from Salmonella enterica serovar Typhimurium LT2, one of the most widely studied microcompartment systems. We first demonstrate that two shell proteins, PduA and PduJ, have a high propensity for self-assembly upon overexpression, and we provide a novel method for self-assembly quantification. Using genomic knock-outs and knock-ins, we systematically show that these two proteins play an essential and redundant role in bacterial microcompartment assembly that cannot be compensated by other shell proteins. At least one of the two proteins PduA and PduJ must be present for the bacterial microcompartment shell to assemble. We also demonstrate that assembly-deficient variants of these proteins are unable to rescue microcompartment formation, highlighting the importance of this assembly property. Our work provides insight into the assembly mechanism of these bacterial organelles and will aid downstream engineering efforts.
蛋白质自组装是一种常见且重要的生物现象，而细菌微室提供了一个研究这一过程的很有前途的模型系统。细菌微室是大型的蛋白质基细胞器，天然地进行着固碳过程，这对于蓝藻和肠道细菌的生存至关重要。由于它们作为纳米生物反应器或药物输送载体的潜在用途，这些结构越来越受到生物工程师的欢迎。然而，由于对这些细菌微室的组装机制的了解有限，限制了将其重新用于非天然功能的努力。在这里，我们全面研究了来自沙门氏菌 Typhimurium LT2 的 1,2-丙二醇利用细菌微室组装涉及的蛋白质，沙门氏菌 Typhimurium LT2 是研究最广泛的微室系统之一。我们首先证明，两种外壳蛋白 PduA 和 PduJ 在过表达时具有很高的自组装倾向，并且我们提供了一种新的自组装定量方法。通过基因组敲除和敲入，我们系统地表明，这两种蛋白质在细菌微室组装中起着必不可少的冗余作用，不能被其他外壳蛋白所补偿。至少有一种 PduA 和 PduJ 蛋白必须存在，细菌微室外壳才能组装。我们还证明，这些蛋白质的组装缺陷变体无法挽救微室的形成，突出了这种组装特性的重要性。我们的工作提供了对这些细菌细胞器组装机制的深入了解，并将有助于下游的工程努力。
