A highly sensitive and specific luminescent MOF determines nitric oxide production and quantifies hydrogen sulfide-mediated inhibition of nitric oxide in living cells.

The synthesis of a novel carboxylate-type organic linker-based luminescent MOF (Zn(H2L) (L1)) (named PUC2) (H2L = 2-aminoterephtalic acid, L1 = 1-(3-aminopropyl) imidazole) is reported by the solvothermal method and comprehensively characterized using single-crystal XRD, PXRD, FTIR, TGA, XPS, FESEM, HRTEM, and BET. PUC2 selectively reacts with nitric oxide (▪NO) with a detection limit of 0.08 µM, and a quenching constant (0.5 × 104 M-1) indicating a strong interaction with ▪NO. PUC2 sensitivity remains unaffected by cellular proteins or biologically relevant metals (Cu2+/ Fe3+/Mg2+/ Na+/K+/Zn2+), RNS/ROS, or H2S to score ▪NO in living cells. Lastly, we used PUC2 to demonstrate that H2S inhibition increases ▪NO production by ~ 14-30% in various living cells while exogenous H2S suppresses ▪NO production, indicating that the modulation of cellular ▪NO production by H2S is rather generic and not restricted to a particular cell type. In conclusion, PUC2 can successfully detect ▪NO production in living cells and environmental samples with considerable potential for its application in improving the understanding of the role of ▪NO in biological samples and study the inter-relationship between ▪NO and H2S.

HupB, a nucleoid-associated protein, is critical for survival of Mycobacterium tuberculosis under host-mediated stresses and for enhanced tolerance to key first-line antibiotics.

To survive and establish its niche, Mycobacterium tuberculosis (Mtb) engages in a steady battle against an array of host defenses and a barrage of antibiotics. Here, we demonstrate that Mtb employs HupB, a nucleoid-associated protein (NAP) as its key player to simultaneously battle and survive in these two stress-inducing fronts. Typically, NAPs are key to bacterial survival under a wide array of environmental or host-mediated stresses. Here, we report that for Mtb to survive under different macrophage-induced assaults including acidic pH, nutrient depletion, oxidative and nitrosative stresses, HupB presence is critical. As expected, the hupB knockout mutant is highly sensitive to these host-mediated stresses. Furthermore, Mtb aptly modulates HupB protein levels to overcome these stresses. We also report that HupB aids Mtb to gain tolerance to high levels of rifampicin (RIF) and isoniazid (INH) exposure. Loss of hupB makes Mtb highly susceptible to even short exposures to reduced amounts of RIF and INH. Overexpressing hupB in Mtb or complementing hupB in the hupB knockout mutant triggers enhanced survival of Mtb under these stresses. We also find that upon loss of hupB, Mtb significantly enhances the permeability of its cell wall by modulating the levels of several surface lipids including phthiocerol dimycocerosates (PDIMs), thus possibly influencing overall susceptibility to host-mediated stresses. Loss of hupB also downregulates efflux pump expression possibly influencing increased susceptibility to INH and RIF. Finally, we find that therapeutic targeting of HupB with SD1, a known small molecule inhibitor, significantly enhances Mtb susceptibility to INH and THP-1 macrophages and significantly reduces MIC to INH. Thus, our data strongly indicate that HupB is a highly promising therapeutic target especially for potential combinatorial shortened therapy with reduced INH and RIF doses.