The C-terminal domain of M. tuberculosis ECF sigma factor I (SigI) interferes in SigI-RNAP interaction

Area of Science:

• Microbiology
• Molecular Biology
• Structural Biology

Background:

• Mycobacterium tuberculosis utilizes ECF sigma factors for adaptation to environmental stress.
• Mtb-SigI, an ECF41 family sigma factor, has uncharacterized roles during stringent response.
• The C-terminal polypeptide extension of Mtb-SigI is structurally and functionally uninvestigated.

Purpose of the Study:

• To elucidate the structural role of the Mtb-SigI C-terminal extension in transcription regulation.
• To characterize the impact of C-terminal truncations on Mtb-SigI interaction with RNA polymerase.
• To understand Mtb-SigI's mechanism in modulating holoenzyme formation.

Main Methods:

• Molecular docking of wild-type and truncated Mtb-SigI with the RNA polymerase β subunit.
• 100 ns molecular dynamics simulations to analyze protein-protein interactions.
• Trajectory analysis to calculate relative binding strengths and assess conformational changes.

Main Results:

• Complete deletion of the Mtb-SigI C-terminal extension significantly enhances binding to core RNA polymerase.
• The C-terminal domain in wild-type Mtb-SigI may impede holoenzyme formation by inducing domain 4 flipping.
• Partial or complete C-terminal deletion reduces domain 4 flipping, facilitating holoenzyme assembly.

Conclusions:

• The C-terminal extension of Mtb-SigI acts as a critical regulator of its interaction with RNA polymerase.
• Modulation of the C-terminal extension influences holoenzyme formation and potentially transcription activity.
• Mtb-SigI's C-terminal domain plays a complex role in transcription regulation, possibly independent of sigma factor antagonists.