The heparin-binding hemagglutinin protein of Mycobacterium tuberculosis is a nucleoid-associated protein.

Nucleoid-associated proteins (NAPs) regulate multiple cellular processes such as gene expression, virulence, and dormancy throughout bacterial species. NAPs help in the survival and adaptation of Mycobacterium tuberculosis (Mtb) within the host. Fourteen NAPs have been identified in Escherichia coli; however, only seven NAPs are documented in Mtb. Given its complex lifestyle, it is reasonable to assume that Mtb would encode for more NAPs. Using bioinformatics tools and biochemical experiments, we have identified the heparin-binding hemagglutinin (HbhA) protein of Mtb as a novel sequence-independent DNA-binding protein which has previously been characterized as an adhesion molecule required for extrapulmonary dissemination. Deleting the carboxy-terminal domain of HbhA resulted in a complete loss of its DNA-binding activity. Atomic force microscopy showed HbhA-mediated architectural modulations in the DNA, which may play a regulatory role in transcription and genome organization. Our results showed that HbhA colocalizes with the nucleoid region of Mtb. Transcriptomics analyses of a hbhA KO strain revealed that it regulates the expression of ∼36% of total and ∼29% of essential genes. Deletion of hbhA resulted in the upregulation of ∼73% of all differentially expressed genes, belonging to multiple pathways suggesting it to be a global repressor. The results show that HbhA is a nonessential NAP regulating gene expression globally and acting as a plausible transcriptional repressor.

Temporal analysis of melanogenesis identifies fatty acid metabolism as key skin pigment regulator.

Therapeutic methods to modulate skin pigmentation has important implications for skin cancer prevention and for treating cutaneous hyperpigmentary conditions. Towards defining new potential targets, we followed temporal dynamics of melanogenesis using a cell-autonomous pigmentation model. Our study elucidates 3 dominant phases of synchronized metabolic and transcriptional reprogramming. The melanogenic trigger is associated with high MITF levels along with rapid uptake of glucose. The transition to pigmented state is accompanied by increased glucose channelisation to anabolic pathways that support melanosome biogenesis. SREBF1-mediated up-regulation of fatty acid synthesis results in a transient accumulation of lipid droplets and enhancement of fatty acids oxidation through mitochondrial respiration. While this heightened bioenergetic activity is important to sustain melanogenesis, it impairs mitochondria lately, shifting the metabolism towards glycolysis. This recovery phase is accompanied by activation of the NRF2 detoxication pathway. Finally, we show that inhibitors of lipid metabolism can resolve hyperpigmentary conditions in a guinea pig UV-tanning model. Our study reveals rewiring of the metabolic circuit during melanogenesis, and fatty acid metabolism as a potential therapeutic target in a variety of cutaneous diseases manifesting hyperpigmentary phenotype.

Conserved and divergent chaperoning effects of Hsp60/10 chaperonins on protein folding landscapes.

The GroEL/ES chaperonin cavity surface charge properties, especially the negative charges, play an important role in its capacity to assist intracavity protein folding. Remarkably, the larger fraction of GroEL/ES negative charges are not conserved among different bacterial species, resulting in a large variation in negative-charge density in the GroEL/ES cavity across prokaryotes. Intriguingly, eukaryotic GroEL/ES homologs have the lowest negative-charge density in the chaperonin cavity. This prompted us to investigate if GroEL's chaperoning mechanism changed during evolution. Using a model in vivo GroEL/ES substrate, we show that the ability of GroEL/ES to buffer entropic traps in the folding pathway of its substrate was partially dependent upon the negative-charge density inside its cavity. While this activity of GroEL/ES was found to be essential for Escherichia coli, it has been perfected in some organisms and diminished in others. However, irrespective of their charges, all the tested homologs retained their ability to regulate polypeptide chain collapse and remove enthalpic traps from folding pathways. The ability of these GroEL/ES homologs to buffer mutational variations in a model substrate correlated with their negative-charge density. Thus, Hsp60/10 chaperonins in different organisms may have changed to accommodate a different spectrum of mutations on their substrates.