How proteins synthesized in the cytoplasm of pathogenic bacteria are able to reach, in an
active way, the cytoplasm of their eukaryotic host cells? In Gram-negative bacteria, this
translocation process is carried out through the Type 3 Secretion System (T3SS), a highly
conserved secretion system composed by more than twenty different proteins. The T3SS
resembles a nano-syringe able to engage the host plasma membrane and allow: 1) The
secretion of toxic proteins through both bacterial membranes, and 2) The translocation of
the bacterial toxins through the host plasma membrane at the “syringe” tip/membrane
interface. Two bacterially encoded proteins are thought to permeabilize the host plasma
membrane to allow translocation through the T3SS. This pair of proteins is highly
conserved among Gram-negative bacteria, suggesting a common mechanism for
protein/toxin translocation. Deletion of either of them completely abolishes bacterial
pathogenicity. Also, it is known that each protein alone is able to form pores in liposomal
membranes.
In order to understand the overall process of protein translocation, we first need to
understand how the translocator proteins are able to spontaneously bind to membranes
and assemble a pore. The focus of my research is to investigate the topology of
membrane bound translocators, and how this topology is affected by other protein factors
involved. Using a Biophysical/Biochemical approach, we will generate valuable
topological data of these translocator proteins.