Mycobacterium tuberculosis WhiB3 responds to O₂ and nitric oxide via its [4Fe-4S] cluster and is essential for nutrient starvation survival

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 28; pp. 11562 - 11567
• Main Authors: Singh, Amit, Guidry, Loni, Narasimhulu, K.V, Mai, Deborah, Trombley, John, Redding, Kevin E, Giles, Gregory I, Lancaster, Jack R. Jr, Steyn, Adrie J.C
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 10.07.2007; National Acad Sciences
• Subjects: Acetates; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bacterial Proteins - physiology; Biochemistry; Biological Sciences; Colony Count, Microbial; Dormancy; Iron - metabolism; Iron-Sulfur Proteins - chemistry; Iron-Sulfur Proteins - metabolism; Iron-Sulfur Proteins - physiology; Metabolism; Mycobacterium tuberculosis; Mycobacterium tuberculosis - genetics; Mycobacterium tuberculosis - growth & development; Mycobacterium tuberculosis - metabolism; Nitric Oxide - metabolism; Nitric Oxide - physiology; Nutrients; Oxidation-Reduction; Oxidative Stress - physiology; Oxygen; Oxygen - metabolism; Oxygen - physiology; Physiological regulation; Saccharomyces cerevisiae Proteins; Sensors; Signal Transduction - physiology; Sulfur - metabolism; Transcription Factors - chemistry; Transcription Factors - metabolism; Transcription Factors - physiology; Type C Phospholipases; Ultraviolet spectroscopy
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0700490104

A fundamental challenge in the redox biology of Mycobacterium tuberculosis (Mtb) is to understand the mechanisms involved in sensing redox signals such as oxygen (O₂), nitric oxide (NO), and nutrient depletion, which are thought to play a crucial role in persistence. Here we show that Mtb WhiB3 responds to the dormancy signals NO and O₂ through its iron-sulfur (Fe-S) cluster. To functionally assemble the WhiB3 Fe-S cluster, we identified and characterized the Mtb cysteine desulfurase (IscS; Rv3025c) and developed a native enzymatic reconstitution system for assembling Fe-S clusters in Mtb. EPR and UV-visible spectroscopy analysis of reduced WhiB3 is consistent with a one-electron reduction of EPR silent [4Fe-4S]²⁺ to EPR visible [4Fe-4S]⁺. Atmospheric O₂ gradually degrades the WhiB3 [4Fe-4S]²⁺ cluster to generate a [3Fe-4S]⁺ intermediate. Furthermore, EPR analysis demonstrates that NO forms a protein-bound dinitrosyl-iron-dithiol complex with the Fe-S cluster, indicating that NO specifically targets the WhiB3 Fe-S cluster. Our data suggest that the mechanism of WhiB3 4Fe-4S cluster degradation is similar to that of fumarate nitrate regulator. Importantly, Mtb ΔwhiB3 shows enhanced growth on acetate medium, but a growth defect on media containing glucose, pyruvate, succinate, or fumarate as the sole carbon source. Our results implicate WhiB3 in metabolic switching and in sensing the physiologically relevant host signaling molecules NO and O₂ through its [4Fe-4S] cluster. Taken together, our results suggest that WhiB3 is an intracellular redox sensor that integrates environmental redox signals with core intermediary metabolism.