Research Interests

image01 1) Metabolism of Mycobacterium tuberculosis :
A) Amino acid metabolism: Fatty acids are thought to act as the primary source of carbon and energy inside host but not much information is available regarding the role of amino acid metabolic pathways in growth and survival of Mtb inside host. We initiated work on this aspect of Mtb metabolism and developed recombinant strains of Mycobacterium tuberculosis H37Ra and Mycobacterium smegmatis for target development and validation studies. We have made considerable progress in identifying the role of putative ORFs and some of them have been functionally/biochemically validated. Our studies with recombinant strains suggest that amino acid metabolic pathways play considerable role in in vitro and ex vivo survival. Apart from being metabolic enzymes they also play key role in other cellular functions and their deletion/down-regulation is manifested in multiple ways. A brief detail of the targets being worked upon and their relevance is detailed below:

  • a) D-amino acid oxidase: D-amino acid oxidases play an important role in converting D-amino acids to their corresponding α-keto acids. MRA_1916 of Mycobacterium tuberculosis H37Ra (Mtb-Ra) is a putative D-amino acid oxidase (DAO). However, its physiological significance including its role in glycine metabolism and other related pathways and how its expression is affected under different physiological stresses encountered by Mtb remains a mystery. Hence, to understand its physiological relevance during mycobacterial growth and survival we initiated this study. We developed a recombinant strain with D-amino oxidase down-regulation and studied effect of carbon source on growth of recombinant strain compared to WT. The results were encouraging and expression studies suggested DAO expression changes under stress (Scientific Reports, 2015).

  • b) Threonine dehydratase: Threonine dehydratase plays an important role in isoleucine biosynthetic process. These are pyridoxal-5-phosphate dependent enzymes. In Mycobacterium tuberculosis H37Ra, MRA_1571 is a putative ORF encoding threonine dehydratase (IlvA). Isoleucine, leucine and valine are branch chain amino acids (BCAAs). BCAAs are important for survival of Mycobacterium tuberculosis inside host and disruption of BCAAs biosynthesis leads to attenuated growth inside host. The BCAAs biosynthetic process is lacking in humans, while, Mtb is capable of meeting its requirement of BCAAs using its biosynthetic capabilities. Targeting BCAAs for drug development purposes is a good strategy as inhibitors targeting this pathway are likely to have lower side effects. Hence, to understand the role of IlvA in Mtb growth we developed a recombinant strain with down-regulated IlvA. Further studies are being undertaken to understand the role of IlvA in Mtb survival during ex vivo and in vivo growth.

  • c) Phosphoserine aminotransferase: The phosphoserine aminotransferase (SerC) catalyzes reversible conversion of 3-phosphohydroxypyruvate to phosphoserine. The phosphoserine aminotransferase of Mycobacterium tuberculosis H37Rv is essential for in vitro survival of Mtb-H37Rv. The Mtb-H37Rv being pathogenic, many avirulent strains including Mtb-H37Ra, M. bovis BCG and M. smegmatis are used for studying the role of metabolic enzymes. We used Mycobacterium smegmatis mc2 155 to study the role of MSMEG_5684, annotated to be a phosphoserine aminotransferase (serC), in growth and serine biosynthesis. To understand the role of SerC in serine biosynthesis and its physiological relevance, we developed a recombinant Mycobacterium smegmatis strain. The recombinant strain shows physiological differences from WT. Further studies are being undertaken to understand the effect of SerC down-regulation on M. smegmatis survival and global role of SerC in bacterial metabolism including serine biosynthesis.

B) Gluconeogenesis: Gluconeogenic pathway is important for routing metabolic intermediates for biomass development when growing on fatty acids as a carbon source. Mtb uses fatty acids as a carbon source. This makes gluconeogenic pathway important for Mtb’s survival inside host and targeting of this pathway may lead to identification of new targets for screening of inhibitors against Mtb. We are developing recombinant bacteria to understand the role of annotated gluconeogenic enzymes in survival and persistence of Mtb.

image01  2) Bioactive metabolites: :
Metabolites of microbial origin can act as potential antibacterial and antitubercular agent. Recent success with semisynthetic spectinamides and teixobactin does suggest that bioactive molecules can be successfully used as an antimicrobial/antitubercular agent. Marine and endophytic bacterial diversity can be a good source of novel metabolites which can be studied for their antitubercular / antibacterial properties.