Chlamydia pneumoniae CopD translocator protein plays a critical role in type III secretion (T3S) and infection

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Pathogenic Gram-negative bacteria utilize type III secretion (T3S) systems to deliver effector proteins into host cells, facilitating infection.
• Chlamydia spp. are obligate intracellular bacteria that employ T3S for host cell invasion, with translocator proteins being crucial components.
• Chlamydia pneumoniae possesses genes for two translocator protein pairs: CopB/CopD and CopB2/CopD2.

Purpose of the Study:

• To investigate the role and interactions of the translocator protein CopD in Chlamydia pneumoniae pathogenesis.
• To identify novel interactions between CopD and other type III secretion system (T3SS) proteins.
• To elucidate the functional significance of CopD in bacterial infectivity.

Main Methods:

• Protein interaction studies to identify novel binding partners of CopD.
• Identification of a specific chaperone binding motif (PxLxxP) in CopD.
• Size exclusion chromatography to analyze CopD and chaperone complex formation.
• In vitro assays using antibodies against CopD to assess its impact on bacterial infectivity.

Main Results:

• Novel interactions were discovered between CopD and three T3SS proteins: CopN, CdsN, and CdsF.
• A putative chaperone binding motif, PxLxxP, was identified in CopD's N-terminal region, essential for binding to the chaperone LcrH_1.
• CopD and LcrH_1 formed unique 1:1 higher-order structures in solution.
• Antibodies targeting CopD reduced Chlamydia pneumoniae infectivity by over 95%.

Conclusions:

• CopD plays a critical role in the pathogenesis of Chlamydia pneumoniae.
• CopD likely functions as a hydrophobic translocator within the bacterial type III secretion system.
• The identified interactions and structural properties provide insights into T3SS mechanism in Chlamydia.