Inositol Monophosphatase: A Bifunctional Enzyme in Mycobacterium smegmatis

Inositol monophosphatase (IMPase) is a crucial enzyme for the biosynthesis of phosphatidylinositol, an essential component in mycobacterial cell walls. IMPase A (ImpA) from Mycobacterium smegmatis is a bifunctional enzyme that also functions as a fructose-1,6-bisphosphatase (FBPase). To better understand the bifunctional nature of this enzyme, point mutagenesis was conducted on several key residues and their enzyme activity was tested. Our results along with active site models support the fact that ImpA is a bifunctional enzyme with residues Gly94, Thr95 hypothesized to be contributing to the FBPase activity and residues Trp220, Asp221 hypothesized to be contributing to the IMPase activity. Double mutants, W220A + D221A reduced both FBPase and IMPase activity drastically while the double mutant G94A + T95A surprisingly partially restored the IMPase activity compared to the single mutants. This study establishes the foundation toward obtaining a better understanding of the bifunctional nature of this enzyme.