Computational methods utilizing the structural and functional information help to understand specific molecular recognition events between the target biomolecule and candidate hits and make it possible to design improved lead molecules for the target.

A small molecule, inhibitor of a protein–protein interaction between the transcription factor Pdr1 and the Med15 subunit of Mediator in the fungal pathogen Candida glabrata, is identified and characterized here; the compound iKIX1 inhibits Pdr1-mediated gene activation and resensitizes drug-resistant C. glabrata to azole antifungals in vitro and in animal models of disseminated and urinary tract infection. Joy Nishikawa et al. report the identification and characterization of a small-molecule inhibitor of a protein–protein interaction between the transcription factor Pdr1 and the MED15 subunit of Mediator in the fungal pathogen Candida glabrata. The lead compound, iKIX1, inhibits Pdr1-mediated gene activation and re-sensitizes drug-resistant C. glabrata to azole antifungals in vitro and in animal models of disseminated and urinary tract infection. The NMR structure of the interaction between Mediator and Pdr1, has also improved our understanding of the mechanism of gene activation by Pdr1 and its inhibition by iKIX1. Eukaryotic transcription activators stimulate the expression of specific sets of target genes through recruitment of co-activators such as the RNA polymerase II-interacting Mediator complex1,2. Aberrant function of transcription activators has been implicated in several diseases. However, therapeutic targeting efforts have been hampered by a lack of detailed molecular knowledge of the mechanisms of gene activation by disease-associated transcription activators. We previously identified an activator-targeted three-helix bundle KIX domain in the human MED15 Mediator subunit that is structurally conserved in Gal11/Med15 Mediator subunits in fungi3,4. The Gal11/Med15 KIX domain engages pleiotropic drug resistance transcription factor (Pdr1) orthologues, which are key regulators of the multidrug resistance pathway in Saccharomyces cerevisiae and in the clinically important human pathogen Candida glabrata5,6. The prevalence of C. glabrata is rising, partly owing to its low intrinsic susceptibility to azoles, the most widely used antifungal agent7,8. Drug-resistant clinical isolates of C. glabrata most commonly contain point mutations in Pdr1 that render it constitutively active9,10,11,12,13,14, suggesting that this transcriptional activation pathway represents a linchpin in C. glabrata multidrug resistance. Here we perform sequential biochemical and in vivo high-throughput screens to identify small-molecule inhibitors of the interaction of the C. glabrata Pdr1 activation domain with the C. glabrata Gal11A KIX domain. The lead compound (iKIX1) inhibits Pdr1-dependent gene activation and re-sensitizes drug-resistant C. glabrata to azole antifungals in vitro and in animal models for disseminated and urinary tract C. glabrata infection. Determining the NMR structure of the C. glabrata Gal11A KIX domain provides a detailed understanding of the molecular mechanism of Pdr1 gene activation and multidrug resistance inhibition by iKIX1. We have demonstrated the feasibility of small-molecule targeting of a transcription factor-binding site in Mediator as a novel therapeutic strategy in fungal infectious disease.

Thermophilic l ‐asparaginases display high stability and activity at elevated temperatures. However, they are of limited use in leukemia therapy because of their low substrate affinity and reduced activity under physiological conditions. In an attempt to combine stability with activity at physiological conditions, 3 active‐site mutants of Pyrococcus furiosus l ‐asparaginase (PfA) were developed. The mutants, specifically K274E, showed improved enzymatic properties at physiological conditions as compared to the wild type. All variants were thermodynamically stable and resistant to proteolytic digestion. None of the enzymes displayed glutaminase activity, a highly desirable therapeutic property. All variants showed higher and significant killing of human cell lines HL60, MCF7, and K562 as compared to the Escherichia coli l ‐asparaginase. Our study revealed that increased substrate accessibility through the active site loop plays a major role in determining activity. A new mechanistic insight has been proposed based on molecular dynamics simulated structures, where dynamic flipping of a critical Tyr residue is responsible for the activity of thermophilic l ‐asparaginases. Our study not only resulted in development of PfA mutants with combination of desirable properties but also gave a mechanistic insight about their activity.—Bansal, S., Srivastava, A., Mukherjee, G., Pandey, R., Verma, A. K., Mishra, P., Kundu, B. Hyperthermophilic asparaginase mutants with enhanced substrate affinity and antineoplastic activity: structural insights on their mechanism of action. FASEB J. 26, 1161‐1171 (2012). www.fasebj.org

The advent of human genome sequencing project has led to a spurt in the number of protein sequences in the databanks. Success of structure based drug discovery severely hinges on the availability of structures. Despite significant progresses in the area of experimental protein structure determination, the sequence-structure gap is continually widening. Data driven homology based computational methods have proved successful in predicting tertiary structures for sequences sharing medium to high sequence similarities. With dwindling similarities of query sequences, advanced homology/ ab initio hybrid approaches are being explored to solve structure prediction problem. Here we describe Bhageerath-H, a homology/ ab initio hybrid software/server for predicting protein tertiary structures with advancing drug design attempts as one of the goals. Bhageerath-H web-server was validated on 75 CASP10 targets which showed TM-scores ≥ 0.5 in 91% of the cases and Cα RMSDs ≤ 5 Å from the native in 58% of the targets, which is well above the CASP10 water mark. Comparison with some leading servers demonstrated the uniqueness of the hybrid methodology in effectively sampling conformational space, scoring best decoys and refining low resolution models to high and medium resolution. Bhageerath-H methodology is web enabled for the scientific community as a freely accessible web server. The methodology is fielded in the on-going CASP11 experiment.