Advances in the assembly model of bacterial type IVB secretion systems

Bacterial type IV secretion systems (T4SSs) are related to not only secretion of effector proteins and virulence factors, but also to bacterial conjugation systems that promote bacterial horizontal gene transfer. The subgroup T4BSS, with a unique mosaic architecture system, consists of nearly 30 proteins that are similar to those from other secretory systems. Despite being intensively studied, the secretion mechanism of T4BSS remains unclear. This review systematically summarizes the protein composition, coding gene set, core complex, and protein interactions of T4BSS. The interactions of proteins in the core complex of the system and the operation mechanism between each element needs to be further studied.