INHIBITION OF ISPD ENZYME TO CONTROL THE GROWTH OF MYCOBACTERIUM TUBERCULOSIS

Manoj Kumar 1 , Pratik Kumar 2 , Pratima Kumari 1 and Jainendra Kumar 3 . 1. Post Graduate Centre & Department of Botany and Biotechnology, College of Commerce, Arts & Science, Patna (Bihar), India 800 020. 2. Intermediate Reference Laboratory, TBDC Campus, Agamkuan, Patna, Bihar 800 007. 3. Ashayan, D.P.R. Colony, Ramjaipal Road, Off West Bailey Road, P.O. Danapur (Bihar) Patna 801503. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Like several other pathogens, Mycobacterium tuberculosis synthesizes isopentenyl diphosphate via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. IspD (2C-methyl-D-erythritol-4-phosphate Cytidyltransferase) is a flexible enzyme that carries out the third step in MEP pathway where 2-C-methyl-D-erythritol 4 phosphate (MEP) condenses with Cytidine Triphosphate (CTP) to form 4diphosphocytidyl-2-amethyl-D-erythritol (CDP-ME). It catalizes the transfer of a cytidyl group from CTP to methylerythritol phosphate and utilizes two substrates, MEP and CTP. Due to this feature, this stage of MEP pathway is a significant reaction step that can be targeted to control the spread of the organism in vivo. Rosuvastatin successfully docks as a ligand close to the active site of the IspD with involvement of low (negative) energy indicating a stable system and a likely binding interaction. It can, thus, be safely assumed that rosuvastatin molecule could possibly be used as a candidate to competitively inhibit IspD to bind to CTP blocking the MEP pathway and keep the proliferating Mycobacterium tuberculosis under control.

Introduction:-
Tuberculosis (TB), caused by the bacterial pathogen Mycobacterium tuberculosis is one of the oldest recorded human ailments and one of the biggest killers among the infectious diseases (Smith, 2003). New vaccines and drugs are needed to control its worldwide epidemic which assumingly kills two million people each year. To develop new anti-tubercular drug candidates, it is essential to understand the genetics and physiology of M. tuberculosis along with its interaction with the host. Search for new molecules that can check the growth and spread of the organism at some early stage of its development is the need of the time. It is urgently required that organism's metabolic targets are identified for novel therapeutics (Brown et al., 2010).
Currently used antibiotics are mostly known to target cell wall biosynthesis in the bacterium. Drugs like isoniazid and ethionamide target the synthesis of mycolic acids and those as ethambutol target arabinogalactan and lipoarabinomannan. A good target might be an enzyme of the Isoprenoid biosynthesis that the organism essentially requires to produce several cellular components including those involved in cell wall formation.
Stage III of the pathway is executed by the enzyme 4-Diphosphocytidyl-2C-methyl-D-erythritol Cytidyltransferase (IspD) which is a homodimer. Each subunit of the dimer is a single domain α/β structure constructed around a seven-stranded twisted β-sheet into which is inserted an extended "β-arm." Two arms associate to form the dimer interface that involves numerous hydrogen bonds and salt bridges (Fig. 1).
The active site is created at the dimer interface by seven polypeptide segments, six from one subunit and one from the partner (Hunter, 2007).  In culture, these compounds displayed nanomolar inhibitory activity preventing the growth of P. falciparum. Imlay et al. (2015) found that Plasmodium IspD could also be an easy intracellular target of MMV008138.