The dynamics and function of stressosome proteins in Listeria monocytogenes

Abstract The human pathogen Listeria monocytogenes is a model microorganism in infection biology. The organism can transform from a saprophyte to an intracellular pathogen and cope with severe environmental challenges, for which the high molecular weight stressosome complex acts as the sensing hub in a complex signal transduction pathway. Yet, little is known of the dynamics, function and localization of the proteins involved in the stress response. We have now determined the dynamics and functional roles of cytosolic, membrane-bound and clustered components of the stressosome complex, using photo-activated localization microscopy (PALM) combined with single-particle tracking (SPT) and single-molecule displacement mapping (SMdM) and supported by physiological studies. We analyzed the stressosome protein RsbR1 and the related blue-light receptor protein RsbL. We find that RsbR1 diffusion is consistently slow, and the protein interacts with the plasma membrane via Prli42. The membrane-bound state of RsbR1 is not required for stress sensing. RsbL diffuses freely in the cytoplasm but associates with the stressosome complex upon exposure to light. The association of RsbL with the stressosome complex is stable and independent of the presence of Prli42. Taken together, our work provides a comprehensive view of the spatial organization and intracellular dynamics of the stressosome proteins in L. monocytogenes, which paves the way towards uncovering the stress sensing mechanism of this signal transduction pathway.