The two-partner secretion pathway in Gram-negative bacteria

我们的研究重点是先前在大肠杆菌O157:H7菌株EDL933基因组注释中描述的TPS系统。我们将该系统的外蛋白和转运体成分分别命名为OtpA和OtpB。我们发现，根据OtpA和OtpB的序列，预测它们不属于TPS系统（溶血素和粘附素）的两个主要亚型之一。尽管如此，我们获得了OtpA和OtpB构成一个真正的双伴侣分泌系统的直接证据。我们发现大肠杆菌O157:H7将OtpA分泌到细胞外环境需要OtpB，而当大肠杆菌K-12菌株产生OtpA时，其分泌严格依赖于OtpB的产生。此外，我们使用OtpA/OtpB作为模型系统来表征通过TPS途径分泌的动力学。尽管外蛋白在挤压到细胞外空间之前必须靶向转运蛋白，但我们发现通过TPS途径的蛋白质分泌非常迅速。最近，我们一直在利用OtpA/OtpB系统来深入了解外蛋白分泌的机制。最值得注意的是，我们已经获得了强有力的证据，证明OtpA是通过两个连续的步骤内膜和外膜运输的。

Our studies have focused on a TPS system that was previously described in the annotation of the genome of E. coli O157:H7 strain EDL933. We designated the exoprotein and transporter components of this system OtpA and OtpB, respectively. We found that OtpA and OtpB are not predicted to belong to either of the two major subtypes of TPS systems (hemolysins and adhesins) based on their sequence. Nevertheless, we obtained direct evidence that OtpA and OtpB constitute a bona fide two-partner secretion system. We found that secretion of OtpA into the extracellular environment in E. coli O157:H7 requires OtpB and that when OtpA is produced in an E. coli K-12 strain, its secretion is strictly dependent on the production of OtpB. Furthermore, we have used OtpA/OtpB as a model system to characterize the kinetics of secretion via the TPS pathway. Despite the fact that the exoprotein must be targeted to the transporter before it is extruded into the extracellular space, we found that protein secretion via the TPS pathway is extremely rapid. Recently, we have been using the OtpA/OtpB system to gain insight into the mechanism of exoprotein secretion. Most notably, we have obtained strong evidence that OtpA is transported across the inner and outer membranes in two sequential steps.