2. Who cares about Rho GTPases?
Clostridium spp.
Salmonella spp.
Bordetella spp. Neisseria spp.

3. Historical GTPase Events
1985 – isolation of Rho = ‘Ras homolog’
1989 – C3 transferase shown to inactivate RhoC => actin disruption in host cells. Isolation of Rac = ‘Ras substrate of C3’.
1990’s – Rho/Rac GTPases shown to act as switches to control membrane receptors and actin cytoskeleton plasticity.

4. Salmonella enterica
Type III Secretion System (TTSS) for translocation of virulence factors

5. Salmonella chaperone proteins

6. …after effector translocation…
Bacterial changes: transient bacterial ‘invasome’ appendages
Host cell changes: macropinocytosis for uptake of Salmonella in nonphagocytic cells
bacterial induced apoptosis in phagocytic cells.

7. Salmonella invasion summary

8. Bacterial Strategies RHO FAMILY GTPASES: Rho, Rac, Cdc42
BACTERIAL INHIBITION OF RHO PROTEINS:
-Large clostridial toxins: Toxin A, B, Lethal Toxin
-C. botulinum C3 transferase
-Salmonella SptP, Yersinia YopE
BACTERIAL ACTIVATION OF RHO PROTEINS:
-E.coli CNF1 and 2 Toxins
-Bordetella dermonecrotizing toxin (DNT)
-Salmonella SopE, Yersinia CNFY

9. Fig. 1. Rho GTPases are targets for bacterial virulence factors.

10. Fig. 2. Bacterial virulence factors affect spatial and temporal regulation of Rho.

11. Why target Rho GTPases? Invasion can be dangerous!
Innate immunity – recognize ‘non-self’ and opsonize for phagocytic cell recognition. LPS recognized by TLRs stimulates NF-KB and leads to transcription of antibacterial factors.
Cell shedding removes adhered bacteria.
Adaptive immunity… takes time.
Virulence factors help microbes invade on their own terms! Rho GTPases are key.

13. Fig. 3. Virulence factors can adapt or mimic eukaryotic mechanisms.

14. How do virulence factors enter?
Toxins
Can act distantly to bacteria because all required elements for virulence self-contained.
Diptheria A-B example:
A region – catalytically active, delivered to cytosol.
B region – for binding host cell and translocating the A-enzymatic fragment to host cytosol at low pH.
Type III or IV Secretion Systems

15. Fig. 4. Domain organization of virulence factors activating or inhibiting Rho GTPases.

16. Fig. 5. Mechanisms to transfer Rho virulence factors into the cell cytosol.

17. Rho Inhibitors Classical model: Large clostridial toxins (LCTs)
Toxins effects were irreversible, while TTSS induced reversible changes in Rho.
Large clostridial toxins (LCTs)
Toxins A, B, Lethal Toxin.
Type Three Secretion Systems
Pseudomonas ExoS, ExoT.
Salmonella SptP, Yersinia YopT, YopE.
C3 transferases, YopT: spatial regulation.

18. Rho activators E.coli CNF, Bordetella DNF: Salmonella SopE, E2:
Block RhoGAP activity so GTPase is permanently active until ubiquitinylation and proteosomal degradation.
Is proteosomal degradation of overactivated Rho a cellular defense that microbes are taking advantage of?
Salmonella SopE, E2:
Rho GEF function to activate Rho but is counterbalanced by SptP GAP activity.

19. Fig. 5. Comparison of activation-deactivation of Rac by Salmonella SopE/Sptp and E. coli CNF1.

20. Why activation/deactivation?
Whether the bacteria supplies the Rho counterbalance (Salmonella) to virulence or the host cell provides it (E.coli)…
-is it simply to return to ‘normal’ cell function?
-or to enhance bacterial uptake?
-or to avoid non-physiologic cell environs that prevent bacterial uptake at all?

21. Summary Rho GTPases can be influenced by:
Activities from separate bacterial factors
Salmonella SopE, SptP; Yersinia YopE,YopT
Dual activity factors
Pseudomonas ExoS, ExoT
Single activity proteins
E. coli CNF1 Toxin
What is the future of the host-pathogen interaction? Extremes vs balance?

22. The End