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Using Mycobacterium smegmatis as a Bioindicator for Zinc-Limited Growth Conditions in Mycobacteria
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Inositol Monophosphatase: A Bifunctional Enzyme in Mycobacterium smegmatis

Rajendra Goswami1, Jasper Marc G Bondoc1, Paul R Wheeler2

  • 1Institute for Tuberculosis Research, College of Pharmacy, and Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, 833 S Wood Street, Chicago, Illinois 60612, United States.

ACS Omega
|November 10, 2018
PubMed

Insights

Mycobacterium smegmatis Inositol monophosphatase A (ImpA) is bifunctional. Key residues were mutated to understand its dual roles, revealing insights into its enzymatic mechanisms and potential drug targets.

Area of Science:

  • Biochemistry
  • Enzymology
  • Molecular Biology

Background:

  • Inositol monophosphatase (IMPase) is vital for phosphatidylinositol synthesis, a key component of mycobacterial cell walls.
  • Inositol monophosphatase A (ImpA) from Mycobacterium smegmatis exhibits bifunctional activity, acting as both IMPase and fructose-1,6-bisphosphatase (FBPase).

Purpose of the Study:

  • To investigate the bifunctional nature of ImpA by identifying key residues responsible for its IMPase and FBPase activities.
  • To elucidate the roles of specific amino acid residues in ImpA's catalytic mechanisms through point mutagenesis.

Main Methods:

  • Site-directed mutagenesis was performed on key residues within the ImpA enzyme.
  • Enzyme activity assays were conducted to assess the IMPase and FBPase activities of wild-type and mutant ImpA proteins.
  • Active site modeling was utilized to support experimental findings.

Main Results:

  • Residues Gly94 and Thr95 were hypothesized to contribute to FBPase activity, while Trp220 and Asp221 were implicated in IMPase activity.
  • Double mutant W220A + D221A significantly reduced both FBPase and IMPase activities.
  • Double mutant G94A + T95A unexpectedly showed partial restoration of IMPase activity compared to single mutants.

Conclusions:

  • This study provides foundational evidence for the bifunctional catalytic mechanisms of ImpA.
  • Specific residues play distinct roles in ImpA's FBPase and IMPase activities, offering targets for further investigation.
  • Understanding ImpA's bifunctionality is crucial for developing novel antimycobacterial strategies.

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