EspM2 is a RhoA guanine nucleotide exchange factor

Area of Science:

• Microbiology
• Cell Biology
• Molecular Biology

Background:

• Type III secretion systems (T3SS) deliver effector proteins into host cells.
• WxxxE effectors are a class of T3SS proteins with diverse functions.
• Rho GTPases are key regulators of the actin cytoskeleton.

Purpose of the Study:

• To investigate the interaction and functional modulation of Rho GTPases by T3SS effectors EspM2 and SifA.
• To determine if EspM2 and SifA possess guanine nucleotide exchange factor (GEF) activity towards Rho GTPases.

Main Methods:

• Protein interaction studies (direct interaction with nucleotide-free RhoA).
• Nuclear Magnetic Resonance (NMR) Spectroscopy to determine protein fold.
• In vitro GEF assays to assess nucleotide exchange on RhoA, Rac1, and H-Ras.
• Site-directed mutagenesis to identify key residues for EspM2 function.
• Ectopic expression in host cells to observe cellular effects (stress fiber formation).

Main Results:

• Both EspM2 and SifA directly bind to nucleotide-free RhoA.
• EspM2 shares a similar fold with SifA and SopE.
• EspM2 exhibits RhoA GEF activity, inducing nucleotide exchange, unlike SifA.
• Mutations in EspM2's WxxxE motif and catalytic loop residues (Q124) attenuate its GEF activity and ability to induce stress fibers.

Conclusions:

• EspM2 functions as a unique RhoA GEF, contributing to stress fiber formation.
• SifA binds RhoA but does not appear to activate it via nucleotide exchange.
• Understanding these effector-GTPase interactions provides insights into bacterial pathogenesis and host cell manipulation.