@article {8097, title = {Identification of key amino acid residues in OqxB mediated efflux of fluoroquinolones using site-directed mutagenesis [Bugworks Research Pvt. Ltd., a C-CAMP Startup]}, journal = {Res Microbiol}, year = {2023}, month = {2023 Feb 02}, pages = {104039}, abstract = {

OqxB belongs to the RND (Resistance-Nodulation-Division) efflux pump family, recognized widely as a major contributor towards enhancing antimicrobial resistance. It is known to be predominantly present in all Klebsiella spp. and is attributed for its role in increasing resistance against an array of antibiotics like nitrofurantoin, quinolones, β-lactams and colistin. However, the presence of oqxB encoding this efflux pump is not limited only to Klebsiella spp., but is also found to occur via horizontal gene transfer in other bacterial genera like Escherichia coli, Enterobacter cloacae and Salmonella spp. Recently, we reported the crystal structure of OqxB and its structure-function relationship required for the efflux of fluoroquinolones. Extending these findings further, we characterized the structural architecture of this efflux pump along with identifying some critical amino acids at the substrate binding domain of OqxB. Based on our in silico modelling studies, both, hydrophobic residues (F180, L280, L621, F626) and polar residues (R48, E50, E184, R157, R774) were found to be located at this site. The present work reports the importance of these key amino acid residues and the crucial ion-pair interactions at the substrate-binding pocket, thereby establishing their role in OqxB mediated efflux and the resultant resistance development against fluoroquinolones.

}, issn = {1769-7123}, doi = {10.1016/j.resmic.2023.104039}, author = {Bhowmik, Purnendu and Bharatham, Nagakumar and Murakami, Satoshi and Ramachandran, Vasanthi and Datta, Santanu} } @article {1858, title = {Azaindole Based Potentiator of Antibiotics against Gram-Negative Bacteria [C-CAMP Startup Bugworks]}, journal = {ACS Infectious Diseases}, year = {2021}, month = {10/2021}, type = {Journal Article}, abstract = {
We discovered azaindole-based compounds with weak innate activity that exhibit substantial potentiation of antibacterial activities of different antibiotics, viz., rifampicin, erythromycin, solithromycin, and novobiocin in Gram-negative bacteria. In the presence of the azaindole derivatives, these antibiotics exhibited submicromolar minimum inhibitory concentrations (MICs) against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. The fold improvements in MIC of these antibiotics that were otherwise weak or inactive on their own against these bacteria were also observed against drug-resistant clinical isolates. Our studies indicate that this selective potentiation is probably through destabilization of the outer membrane{\textquoteright}s integrity, known to be regulated by the lipopolysaccharides (LPS). Thus, the azaindole based compounds described here open opportunities for those antibiotics that are otherwise ineffective due to LPS mediated entry barriers in Gram-negative bacteria.
}, keywords = {Azaindole, Bacterial Permeability, Lipopolysachhardies (LPS), Polymyxin, Synergy}, doi = {10.1021/acsinfecdis.1c00171}, url = {https://pubs.acs.org/doi/abs/10.1021/acsinfecdis.1c00171$\#$}, author = {Sharma, Sreevalli and Rao, Ranga and Reeve, Stephanie M and Phelps, Gregory A and Bharatham, Nagakumar and Katagihallimath, Nainesh and Ramachandran, Vasanthi and Raveendran, Savitha and Sarma, Maitrayee and Nath, Anubha} } @article {1861, title = {Structure and function relationship of OqxB efflux pump from Klebsiella pneumoniae [Bugworks, a C-CAMP startup]}, journal = {Nature communications}, volume = {12}, year = {2021}, month = {09/2021}, pages = {1{\textendash}12}, type = {Journal Article}, abstract = {

OqxB is an RND (Resistance-Nodulation-Division) efflux pump that has emerged as a factor contributing to the antibiotic resistance in Klebsiella pneumoniae. OqxB underwent horizontal gene transfer and is now seen in other Gram-negative bacterial pathogens including Escherichia coli, Enterobacter cloacae and Salmonella spp., further disseminating multi-drug resistance. In this study, we describe crystal structure of OqxB with n-dodecyl-β-D-maltoside (DDM) molecules bound in its substrate-binding pocket, at 1.85 {\r A} resolution. We utilize this structure in computational studies to predict the key amino acids contributing to the efflux of fluoroquinolones by OqxB, distinct from analogous residues in related transporters AcrB and MexB. Finally, our complementation assays with mutated OqxB and minimum inhibitory concentration (MIC) experiments with clinical isolates of E. coli provide further evidence that the predicted structural features are indeed involved in ciprofloxacin efflux.

}, doi = {https://doi.org/10.1038/s41467-021-25679-0}, url = {https://www.nature.com/articles/s41467-021-25679-0}, author = {Bharatham, Nagakumar and Bhowmik, Purnendu and Aoki, Maho and Okada, Ui and Sharma, Sreevalli and Yamashita, Eiki and Shanbhag, Anirudh P and Rajagopal, Sreenath and Thomas, Teby and Sarma, Maitrayee and others} } @article {764, title = {Nitrothiophene carboxamides, a novel narrow spectrum antibacterial series: Mechanism of action and Efficacy [Bugworks Res. Pvt. Ltd., a C-CAMP Startup]}, journal = {Sci Rep}, volume = {8}, year = {2018}, month = {2018 May 08}, pages = {7263}, abstract = {

The mechanism of efflux is a tour-de-force in the bacterial armoury that has thwarted the development of novel antibiotics. We report the discovery of a novel chemical series with potent antibacterial properties that was engineered to overcome efflux liability. Compounds liable to efflux specifically via the Resistance Nodulation and cell Division (RND) pump, AcrAB-TolC were chosen for a hit to lead progression. Using structure-based design, the compounds were optimised to lose their binding to the efflux pump, thereby making them potent on wild-type bacteria. We discovered these compounds to be pro-drugs that require activation in E. coli by specific bacterial nitroreductases NfsA and NfsB. Hit to lead chemistry led to the generation of compounds that were potent on wild-type and multi-drug resistant clinical isolates of E. coli, Shigella spp., and Salmonella spp. These compounds are bactericidal and efficacious in a mouse thigh infection model.

}, issn = {2045-2322}, doi = {10.1038/s41598-018-25407-7}, author = {Hameed P, Shahul and Bharatham, Nagakumar and Katagihallimath, Nainesh and Sharma, Sreevalli and Nandishaiah, Radha and Shanbhag, Anirudh P and Thomas, Teby and Narjari, Riya and Sarma, Maitrayee and Bhowmik, Purnendu and Amar, Prakruthi and Ravishankar, Rajani and Jayaraman, Ramesh and Muthan, Kubendran and Subbiah, Ramesh and Ramachandran, Vasanthi and Balasubramanian, V and Datta, Santanu} } @article {742, title = {The role of ZA channel water-mediated interactions in the design of bromodomain-selective BET inhibitors.}, journal = {J Mol Graph Model}, volume = {81}, year = {2018}, month = {2018 Mar 22}, pages = {197-210}, abstract = {

The Bromodomain and Extra-Terminal domain (BET) family of proteins are involved in the regulation of gene transcription, and their dysregulation is implicated in several diseases including cancer. BET proteins contain two tandem bromodomains (BD1 and BD2) that independently recognize acetylated-lysine residues and appear to have distinct biological roles. We compared several published co-crystal structures and found five positions near the substrate binding pocket that vary between BET bromodomains. One position located in the ZA loop has unique properties. In BRD2-4, this residue is glutamine in BD1 and lysine in BD2; in BRDT, this residue is arginine in BD1 and asparagine in BD2. Using molecular modeling, we identified differences in the water-mediated network at this position between bromodomains. Molecular dynamics simulations helped rationalize the observed bromodomain selectivity for exemplar BET inhibitors and a congeneric series of tetrahydroquinolines (THQ) that differed by a single heteroatom near the ZA channel. The 2-furan SJ830599, the most BD2-selective THQ analog, did not disrupt the water-mediated networks in either domain, but was electrostatically-repulsed by the specific arrangement of the W5 water dipole in BD1. Our work underscores the value of exploring water-mediated interactions to study ligand binding, and highlights the difficulty of optimizing polar interactions due to high desolvation penalties. Finally, we suggest further modifications to THQ-based BET inhibitors that would increase BD2-selectivity in BRD2-4, while minimizing affinity for one or both bromodomains of BRDT.

}, issn = {1873-4243}, doi = {10.1016/j.jmgm.2018.03.005}, author = {Bharatham, Nagakumar and Slavish, Peter J and Young, Brandon M and Shelat, Anang A} } @article {889, title = {A strategy to identify a ketoreductase that preferentially synthesizes pharmaceutically relevant (S)-alcohols using whole-cell biotransformation [Bugworks Res. Pvt. Ltd., a C-CAMP Startup]}, journal = {Microb Cell Fact}, volume = {17}, year = {2018}, month = {2018 Dec 03}, pages = {192}, abstract = {

INTRODUCTION: Chemical industries are constantly in search of an expeditious and environmentally benign method for producing chiral synthons. Ketoreductases have been used as catalysts for enantioselective conversion of desired prochiral ketones to their corresponding alcohol. We chose reported promiscuous ketoreductases belonging to different protein families and expressed them in E.\ coli to evaluate their ability as whole-cell catalysts for obtaining chiral alcohol intermediates of pharmaceutical importance. Apart from establishing a method to produce high value (S)-specific alcohols that have not been evaluated before, we propose an in silico analysis procedure\ to predict product chirality.

RESULTS: Six enzymes originating from Sulfolobus\ sulfotaricus, Zygosaccharomyces\ rouxii, Hansenula\ polymorpha, Corynebacterium sp. ST-10, Synechococcus sp. PCC\ 7942 and Bacillus sp. ECU0013 with reported efficient activity for dissimilar substrates are compared here to arrive at an optimal enzyme for the method. Whole-cell catalysis of ketone intermediates for drugs like Aprepitant, Sitagliptin and Dolastatin using E.\ coli over-expressing these enzymes yielded (S)-specific chiral alcohols. We explain this chiral specificity for the best-performing enzyme, i.e., Z.\ rouxii ketoreductase using in silico modelling and MD simulations. This rationale was applied to five additional ketones that are used in the synthesis of Crizotinib, MA-20565\ (an antifungal agent), Sulopenem, Rivastigmine, Talampanel and Barnidipine and predicted the yield of (S) enantiomers. Experimental evaluation matched the in silico analysis wherein ~ 95\% (S)-specific alcohol with a chemical yield of 23-79\% was obtained through biotransformation. Further, the cofactor re-cycling was optimized by switching the carbon source from glucose to sorbitol that improved the chemical yield to 85-99\%.

CONCLUSIONS: Here, we present a strategy to synthesize pharmaceutically relevant chiral alcohols by ketoreductases using a cofactor balanced whole-cell catalysis scheme that is useful for the industry. Based on the results obtained in these trials, Zygosaccharomyces\ rouxii ketoreductase was identified as a proficient enzyme to obtain (S)-specific alcohols from their respective ketones. The whole-cell catalyst when combined with nutrient modulation of using sorbitol as a carbon source helped obtain high enantiomeric and chemical yield.

}, issn = {1475-2859}, doi = {10.1186/s12934-018-1036-2}, author = {Haq, Saiful F and Shanbhag, Anirudh P and Karthikeyan, Subbulakshmi and Hassan, Imran and Thanukrishnan, Kannan and Ashok, Abhishek and Sukumaran, Sunilkumar and Ramaswamy, S and Bharatham, Nagakumar and Datta, Santanu and Samant, Shalaka and Katagihallimath, Nainesh} } @article {524, title = {Delineating Substrate Diversity of Disparate Short-Chain Dehydrogenase Reductase from Debaryomyces hansenii [Bugworks Res. Pvt. Ltd., a C-CAMP Startup]}, journal = {PLoS One}, volume = {12}, year = {2017}, month = {2017}, pages = {e0170202}, abstract = {

Short-chain dehydrogenase reductases (SDRs) have been utilized for catalyzing the reduction of many aromatic/aliphatic prochiral ketones to their respective alcohols. However, there is a paucity of data that elucidates their innate biological role and diverse substrate space. In this study, we executed an in-depth biochemical characterization and substrate space mapping (with 278 prochiral ketones) of an unannotated SDR (DHK) from Debaryomyces hansenii and compared it with structurally and functionally characterized SDR Synechococcus elongatus. PCC 7942 FabG to delineate its industrial significance. It was observed that DHK was significantly more efficient than FabG, reducing a diverse set of ketones albeit at higher conversion rates. Comparison of the FabG structure with a homology model of DHK and a docking of substrate to both structures revealed the presence of additional flexible loops near the substrate binding site of DHK. The comparative elasticity of the cofactor and substrate binding site of FabG and DHK was experimentally substantiated using differential scanning fluorimetry. It is postulated that the loop flexibility may account for the superior catalytic efficiency of DHK although the positioning of the catalytic triad is conserved.

}, issn = {1932-6203}, doi = {10.1371/journal.pone.0170202}, author = {Ghatak, Arindam and Bharatham, Nagakumar and Shanbhag, Anirudh P and Datta, Santanu and Venkatraman, Janani} } @article {645, title = {Performance of a docking/molecular dynamics protocol for virtual screening of nutlin-class inhibitors of Mdmx.}, journal = {J Mol Graph Model}, volume = {74}, year = {2017}, month = {2017 Jun}, pages = {54-60}, abstract = {

A virtual screening protocol involving docking and molecular dynamics has been tested against the results of fluorescence polarization assays testing the potency of a series of compounds of the nutlin class for inhibition of the interaction between p53 and Mdmx, an interaction identified as a driver of certain cancers. The protocol uses a standard docking method (AutoDock) with a cutoff based on the AutoDock score (ADscore), followed by molecular dynamics simulation with a cutoff based on root-mean-square-deviation (RMSD) from the docked pose. An analysis of the experimental and computational results shows modest performance of ADscore alone, but dramatically improved performance when RMSD is also used.

}, issn = {1873-4243}, doi = {10.1016/j.jmgm.2017.02.014}, author = {Bharatham, Nagakumar and Finch, Kristin E and Min, Jaeki and Mayasundari, Anand and Dyer, Michael A and Guy, R Kiplin and Bashford, Donald} }