Polypharmacological repurposing approach identifies approved drugs as potential inhibitors of Mycobacterium tuberculosis.

Mycobacterium tuberculosis (M. tb), the causative pathogen of tuberculosis (TB) remains the leading cause of death from single infectious agent. Furthermore, its evolution to multi-drug resistant (MDR) and extremely drug-resistant (XDR) strains necessitate de novo identification of drug-targets/candidates or to repurpose existing drugs against known targets through drug repurposing. Repurposing of drugs has gained traction recently where orphan drugs are exploited for new indications. In the current study, we have combined drug repurposing with polypharmacological targeting approach to modulate structure-function of multiple proteins in M. tb. Based on previously established essentiality of genes in M. tb, four proteins implicated in acceleration of protein folding (PpiB), chaperone assisted protein folding (MoxR1), microbial replication (RipA) and host immune modulation (S-adenosyl dependent methyltransferase, sMTase) were selected. Genetic diversity analyses in target proteins showed accumulation of mutations outside respective substrate/drug binding sites. Using a composite receptor-template based screening method followed by molecular dynamics simulations, we have identified potential candidates from FDA approved drugs database; Anidulafungin (anti-fungal), Azilsartan (anti-hypertensive) and Degarelix (anti-cancer). Isothermal titration calorimetric analyses showed that the drugs can bind with high affinity to target proteins and interfere with known protein-protein interaction of MoxR1 and RipA. Cell based inhibitory assays of these drugs against M. tb (H37Ra) culture indicates their potential to interfere with pathogen growth and replication. Topographic assessment of drug-treated bacteria showed induction of morphological aberrations in M. tb. The approved candidates may also serve as scaffolds for optimization to future anti-mycobacterial agents which can target MDR strains of M. tb.

The Salmonella typhi Cell Division Activator Protein StCAP Impacts Pathogenesis by Influencing Critical Molecular Events.

Conserved molecular signatures in multidrug-resistant Salmonella typhi can serve as novel therapeutic targets for mitigation of infection. In this regard, we present the S. typhi cell division activator protein (StCAP) as a conserved target across S. typhi variants. From in silico and fluorimetric assessments, we found that StCAP is a DNA-binding protein. Replacement of the identified DNA-interacting residue Arg34 of StCAP with Ala34 showed a dramatic (15-fold) increase in Kd value compared to the wild type (Kd 546 nm) as well as a decrease in thermal stability (10 °C shift). Out of the two screened molecules against the DNA-binding pocket of StCAP, eltrombopag, and nilotinib, the former displayed better binding. Eltrombopag inhibited the stand-alone S. typhi culture with an IC50 of 38 µM. The effect was much more pronounced on THP-1-derived macrophages (T1Mac) infected with S. typhi where colony formation was severely hindered with IC50 reduced further to 10 µM. Apoptotic protease activating factor1 (Apaf1), a key molecule for intrinsic apoptosis, was identified as an StCAP-interacting partner by pull-down assay against T1Mac. Further, StCAP-transfected T1Mac showed a significant increase in LC3 II (autophagy marker) expression and downregulation of caspase 3 protein. From these experiments, we conclude that StCAP provides a crucial survival advantage to S. typhi during infection, thereby making it a potent alternative therapeutic target.

Ocular protein optineurin shows reversibility from unfolded states and exhibits chaperone-like activity.

Optineurin (OPTN) is a multifunctional, ubiquitously expressed cytoplasmic protein, mutants of which are associated with primary open-angle glaucoma (POAG) and amyotrophic lateral sclerosis (ALS). The most abundant heat shock protein crystallin, known for its remarkable thermodynamic stability and chaperoning activity, allows ocular tissues to withstand stress. The presence of OPTN in ocular tissues is intriguing. Interestingly, OPTN also harbors heat shock elements in its promoter region. Sequence analysis of OPTN exhibits intrinsically disordered regions and nucleic acid binding domains. These properties hinted that OPTN might be endowed with sufficient thermodynamic stability and chaperoning activity. However, these attributes of OPTN have not yet been explored. Here, we studied these properties through thermal and chemical denaturation experiments and monitored the processes using CD, fluorimetry, differential scanning calorimetry, and dynamic light scattering. We found that upon heating, OPTN reversibly forms higher-order multimers. OPTN also displayed a chaperone-like function by reducing the thermal aggregation of bovine carbonic anhydrase. It regains its native secondary structure, RNA-binding property, and melting temperature (T m) after refolding from a thermally as well as chemically denatured state. From our data, we conclude that OPTN, with its unique ability to revert from the stress-mediated unfolded state and its unique chaperoning function, is a valuable protein of the ocular tissues.