Figure 8.

Schematic illustration of the role of YscF needle polymerization in Yop secretion and translocation. In a first step, the bacterium forms the necessary inner and outer membrane components of the translocation machinery and attaches to the host cell surface with adhesion proteins such as YadA. This host cell contact or chemical signals of the medium trigger the formation of the needle by polymerization of YscF, which serves as a driving force to puncture the host cell membrane. Thereby a continuous conduit is formed from the bacterial surface to the host cell cytoplasm for Yop translocation. The dotted lines indicate that the outer and inner membrane components might interact in the absence of the needle. YscC, outer membrane protein channel; YscN, putative ATPase.