Protein kinase G confers survival advantage to Mycobacterium tuberculosis during latency-like conditions

Abstract

Protein Kinase G (PknG), a thioredoxin-fold containing eukaryotic like serine/threonine protein kinase (STPK), is a virulence factor in the Mycobacterium tuberculosis, required for inhibition of phago-lysosomal fusion. Here, we unravelled novel functional facets of PknG during latency like conditions. We find that PknG mediates persistence under stressful conditions like hypoxia and abets drug tolerance. PknG mutant displayed minimal growth in nutrient limiting conditions suggesting its role in modulating cellular metabolism. Intracellular metabolic profiling revealed that PknG is necessary for efficient metabolic adaptation during hypoxia. Notably, PknG mutant exhibited reductive shift in mycothiol redox potential (EMSH) and compromised stress response. Exposure to antibiotics and hypoxic environment resulted in higher oxidative shift in EMSH of PknG mutant compared with the wild type. Persistence during latency like conditions required kinase activity and thioredoxin motifs of PknG and is mediated through phosphorylation of a central metabolic regulator GarA. Finally, using guinea pig model of infection, we assessed the in-vivo role of PknG in manifestation of disease pathology and established a role for PknG in stable granuloma formation, hallmark structures of latent tuberculosis. Taken together, PknG mediated GarA phosphorylation is important for maintenance of both mycobacterial physiology and redox poise, an axis which is dispensable for survival under normoxic conditions but is critical for non-replicating persistence of mycobacteria. In conclusion, we propose that PknG likely acts as modulator of latency-associated signals.