Biochemical and structural insights into microtubule perturbation by CopN from Chlamydia pneumoniae

Area of Science:

• Microbiology
• Cell Biology
• Structural Biology

Background:

• Pathogens often target the host actin network, but microtubule disruption is less common.
• Chlamydia species possess proteins, like pCopN from C. pneumoniae, that interact with tubulin.
• CopN is confirmed as a Chlamydia homolog of the LcrE family, regulating type III secretion.

Purpose of the Study:

• To investigate the molecular mechanism by which pCopN inhibits microtubule assembly.
• To elucidate the structural basis of CopN's interaction with tubulin.
• To explore functional divergence of CopN proteins within Chlamydia species.

Main Methods:

• In vitro tubulin binding and microtubule assembly assays.
• Structural analysis of pCopN and comparison with MxiC.
• Identification of the minimal tubulin-binding region of pCopN.

Main Results:

• pCopN delays microtubule nucleation and sequesters tubulin at steady state.
• It binds the β subunit interface, inhibiting nucleotide exchange and longitudinal self-association.
• The minimal tubulin-binding region resides in the second and third helical repeats of pCopN.
• CopN from C. trachomatis does not bind tubulin, indicating functional divergence.

Conclusions:

• C. pneumoniae CopN inhibits microtubule assembly by sequestering tubulin and blocking nucleotide exchange.
• CopN proteins have evolved distinct functions beyond type III secretion regulation.
• The findings provide a mechanistic understanding of C. pneumoniae CopN's effect on host microtubules.