The transport of proteins across the bacterial cell envelope is mediated by protein complexes called specialized secretion systems. These nanomachines exist in both Gram-positive and Gram-negative bacteria and have been categorized into different types based on their structural components and function. Interestingly, multiple studies suggest the existence of a protein complex in endospore-forming bacteria that appears to be a new type of specialized secretion system. This protein complex is called the SpoIIIA-SpoIIQ complex and is an exception to the categorical norm since it appears to be a hybrid composed of different parts from well-defined specialized secretion systems. Here we summarize and discuss the current understanding of this complex and its potential role as a specialized secretion system.

蛋白质跨细菌细胞膜的运输是由称为特殊分泌系统的蛋白质复合物介导的。这些纳米机器既存在于革兰氏阳性细菌中，也存在于革兰氏阴性细菌中，并根据其结构成分和功能分为不同的类型。有趣的是，多项研究表明，在形成内生孢子的细菌中存在蛋白质复合物，这似乎是一种新型的专门分泌系统。这种蛋白质复合物称为SpoIIIA-SpoIIQ复合物，是分类规范的一个例外，因为它似乎是由明确定义的专门分泌系统的不同部分组成的杂种。在这里，我们总结并讨论了对该复合物的当前理解及其作为特殊分泌系统的潜在作用。