Structural insight into the heme-based redox sensing by DosS from Mycobacterium tuberculosis

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Mycobacterium tuberculosis enters a non-replicating persistence state under hypoxia or nitric oxide (NO).
• This transformation is mediated by sensor histidine kinases DosS and DosT, which possess GAF domains for oxygen tension detection.

Purpose of the Study:

• Determine the crystal structure of the GAF-A domain of DosS.
• Investigate the interaction of the GAF-A domain with heme and its role in sensing oxygen levels.

Main Methods:

• Crystal structure determination of the GAF-A domain of DosS.
• Analysis of heme interaction, coordination, and redox properties within the GAF-A domain.
• Investigating the effect of flavin nucleotides and NADH on DosS heme reduction.

Main Results:

• The crystal structure revealed a b-type heme embedded in a hydrophobic cavity of the GAF-A domain.
• The heme iron's coordination state changed upon reduction and oxidation, with limited O(2) binding.
• A hydrogen bond network facilitates electron transfer, explaining DosS's inability to bind O(2).
• Flavin nucleotides reduced the heme iron, while NADH did not.

Conclusions:

• DosS functions as a redox sensor, detecting hypoxic conditions through heme reduction.
• The structural and biochemical data provide insights into the mechanism of hypoxia sensing in M. tuberculosis.