Evolutionarily divergent Mycobacterium tuberculosis CTP synthase filaments are under selective pressure

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Cytidine triphosphate synthase (CTPS) is essential for Mycobacterium tuberculosis viability, producing cytidine triphosphate (CTP) vital for nucleic acid and cell wall synthesis.
• CTPS typically forms higher-order filaments in various organisms, suggesting a similar structure in M. tuberculosis.

Purpose of the Study:

• To investigate the higher-order structure of M. tuberculosis CTPS (mtCTPS) and its functional implications.
• To explore the role of mtCTPS filamentation in enzyme activity, localization, and bacterial survival.

Main Methods:

• Structural analysis
• Biochemical assays
• Cellular imaging techniques
• Analysis of clinical isolates

Main Results:

• mtCTPS assembles into filaments with a unique architecture, distinct from other organisms.
• Filament polymerization stabilizes the active enzyme conformation, enhances localized CTP production, and resists product inhibition.
• mtCTPS filaments localize near the CTP-dependent chromosome segregation complex, and impaired polymerization affects this complex formation.
• Mutants preventing filament formation are positively selected in clinical M. tuberculosis isolates.

Conclusions:

• mtCTPS utilizes an unusual filamentation mechanism for spatially organized CTP production, essential for M. tuberculosis.
• This filamentation is critical for bacterial survival under host and antibiotic pressures, presenting a potential therapeutic target.