Bacterial toxins inhibiting or activating small GTP-binding proteins

Area of Science:

• Microbiology
• Cell Biology
• Biochemistry

Background:

• Small GTPases, including Ras and Rho families, are crucial regulators of cellular processes.
• Specific amino acid residues in switch 1 and switch 2 domains are vulnerable to bacterial toxin modification.
• Rho GTPases play key roles in cell membrane dynamics and downstream signaling pathways.

Purpose of the Study:

• To review the molecular mechanisms by which bacterial toxins target and modify Rho GTPases.
• To highlight the diverse enzymatic activities employed by toxins to disrupt Rho GTPase function.
• To discuss the implications of these modifications on cellular signaling.

Main Methods:

• Analysis of published literature on bacterial toxins affecting Rho GTPases.
• Description of enzymatic modifications: ADP-ribosylation, glucosylation, and deamidation.
• Identification of specific target amino acids and their functional consequences.

Main Results:

• Exoenzyme C3 (Clostridium botulinum) ADP-ribosylates Rho at R43, inhibiting membrane recruitment.
• Clostridium difficile toxin B and Clostridium sordellii lethal toxin glucosylate Rho, Rac, and Cdc42, blocking effector binding.
• Cytotoxic necrotizing factor 1 (CNF1) deamidates Rho at Q63, preventing GTPase activity and causing permanent activation.

Conclusions:

• Rho GTPases are targeted by at least three distinct bacterial toxin activities.
• Toxin-mediated modifications effectively inhibit or constitutively activate Rho GTPases, leading to cellular dysfunction.
• Understanding these mechanisms provides insights into bacterial pathogenesis and host-pathogen interactions.