Graduate Students Mini Symposium VII - 2024

01:15 PM Lisa Werland (PG Yuan)
The regulation dynamics of the PhoQ sensor kinase by small proteins in E. coli

In E. coli, the PhoQ/PhoP two-component system (TCS) senses host-associated signals and is crucial for virulence regulation. Two small proteins regulate the sensor kinase PhoQ: MgrB inhibits PhoQ while SafA activates PhoQ. The dynamics of regulation by MgrB and SafA have not been studied systematically, and the interrelation between these opposing regulations remains unknown. We investigate changes in the interaction between PhoQ and the small proteins under extracellular conditions that mimic the mammalian host environment. The results suggest that MgrB and SafA utilise divergent mechanisms to regulate their target protein PhoQ but co-regulate under conditions where both are expressed.

01:45 PM David Rodríguez Méndez (MPRG Höfer)
NudC mediated decapping of 5’-NAD-RNA: Mechanisms and functional implications

In E. coli, NudC mediates the decapping process of 5’-NAD-RNA. Resulting in the hydrolytic decapping of 5’-NAD-RNA, producing 5’-P-RNA and NMN. Alphafold3 predictions and crystal structure analyses indicated that NudC-RNA interaction is coordinated by R120 and R122 through electrostatic interactions. Mutational analysis on such residues, demonstrated a decreased affinity towards NAD-RNA, while prevailing catalytic activity on NAD. Moreover, single-molecule tracking studies revealed that RNA interaction promotes NudC membrane localization, suggesting interactions with membrane-localized partners and possible links to transcriptional and translational processes. These findings provide new insights into the mechanisms of NAD-RNA decapping and its biological implications.

02:15 PM Sebastian Großmann (AG Diepold)
Revealing the localization and function of the gatekeepers of the type III secretion system using optogenetic tools

Many Gram-negative bacteria use a type III secretion system to manipulate eukaryotic cells. A gatekeeper complex blocks premature secretion and is essential for a successful infection. Using live cell microscopy, we found that in Yersinia enterocolitica, all gatekeeper proteins localize in the bacterial cytosol. Applying and adapting optogenetic methods, we succeeded to control individual gatekeepers in a reversible manner. Sequestration of the gatekeepers led to uncontrolled secretion, indicating that they are prevented from carrying out their regulatory function. Interestingly, this control required the sequestration of gatekeepers to a liquid-liquid phase separation compartment, while sequestration to the membrane did not impede their function.