V. Nagaraja Ph.D.
Professor, Indian Institute of Science, Bengaluru, India
Perturbation of DNA topology in mycobacteria
To maintain the topological homeostasis of the genome in the cell, DNA topoisomerases catalyse DNA cleavage, strand passage and rejoining of the ends. Thus, although they are essential house- keeping enzymes, they are the most vulnerable targets; arrest of the reaction after the first trans-esterification step leads to breaks in DNA and cell death. Some of the successful antibacterial or anticancer drugs target the step ie arrest the reaction or stabilize the topo -DNA covalent complex. I will describe our efforts in this direction – to target DNA gyrase and also topoisomerase1 from mycobacteria. The latter, although essential, has no inhibitors described so far. The new inhibitors being characterized are also used to probe topoisomerase control of gene expression.
In the biological warfare between the organisms, a diverse set of molecules encoded by invading genomes target the above mentioned most vulnerable step of topoisomerase reaction, leading to the accumulation of double strand breaks. Bacteria, on their part appear to have developed defense strategies to protect the cells from genomic double strand breaks. I will describe a mechanism involving three distinct gyrase interacting proteins which inhibit the enzyme in vitro. However, in vivo all these topology modulators protect DNA gyrase from poisoning effect by sequestering the enzyme away from DNA.
Next, we have targeted a topology modulator protein, a nucleoid associated protein(NAP) from Mycobacterium tuberculosis to develop small molecule inhibitors by structure based design. Over expression of HU leads to alteration in the nucleoid architecture. The crystal structure of the N-terminal half of HU reveals a cleft that accommodates duplex DNA. Based on the structural feature, we have designed inhibitors which bind to the protein and affect its interaction with DNA, de-compact the nucleoid and inhibit cell growth. Chemical probing with the inhibitors reveal the importance of HU regulon in M.tuberculosis.
Nitish Sathyanrayanan, Sandesh Ganji and Holenarsipur Gundurao Nagendra.
Insilico Analysis of hypothetical proteins from Leishmania donovani: A Case study of a membrane protein of the MFS class reveals their plausible roles in drug resistance
Kala-azar or visceral leishmaniais (VL), caused by protozoan parasite Leishmania donovani, is one of the leading causes of morbidity and mortality in Bihar, India (Guerin et al. 2002; Mubayi et al. 2010). The disease is transmitted to the humans mainly by the vector, Phlebotmus argentipes, commonly known as Sand fly. The majority of VL (> 90%) occurs in only six countries: Bangladesh, India, Nepal, Sudan, Ethiopia and Brazil (Chappuis et al. 2007). In the Indian subcontinent, about 200 million people are estimated to be at risk of developing VL and this region harbors an estimated 67% of the global VL disease burden. The Bihar state only has captured almost 50% cases out of total cases in Indian sub-continent (Bhunia et al. 2013). ‘Conserved hypothetical’ proteins pose a challenge not just to functional genomics, but also to biology in general (Galperin and Koonin 2004). Leishmania donovani (strain BPK282A1) genome consists of a staggering ∼65% of hypothetical proteins. These uncharacterized proteins may enable better appreciation of signalling pathways, general metabolism, stress response and even drug resistance.