Short talk:
The dynamic exchange of core components of the type III secretion system shapes its assembly and function

Andreas Diepold1

1Max Planck Institute for Terrestrial Microbiology, Marburg, Germany

To interact with and influence their environment, bacteria have evolved a variety of secretion systems. These systems enable the specific transport of proteins across bacterial membrane(s) and into target cells. Secretion systems are important weapons for pathogens, but also shape bacterial communities by mediating competition or symbiosis. Key secretion systems have been characterized in structural detail and appear as defined, apparently stable protein complexes. However, this impression can be deceiving. Like many biological processes, protein secretion is inherently dynamic and adaptive at multiple levels, and subunits exchange during the assembly and function of the secretion systems. In the type III secretion system (T3SS), we found that essential cytosolic subunits are not only exchanged with a pool of freely diffusing molecules, but that this exchange is linked to the function of the T3SS, protein secretion. We verified and exploited this finding by implementing an optogenetic interaction switch with one of the dynamic components to control T3SS activity with high spatial and temporal precision. Bacteria benefit from these protein dynamics: the exchange allows them to adapt T3SS activity to external conditions much more rapidly than other mechanisms. Surprisingly, we now discovered that protein exchange is not limited to the cytosolic subunits of the T3SS, but also occurs in key structural components of the system. This dynamic behavior supports the assembly and strongly influences the function and regulation of the system. Our data provide a new view of the molecular working mechanism of the T3SS and highlight the physiological importance of protein dynamics for bacterial secretion systems and other molecular machines.


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