Title page for ETD etd-07022012-113304


Type of Document Dissertation
Author Nourbakhsh, Aida
URN etd-07022012-113304
Title Molecular Characterization of Inositol Monophosphatase Like Enzymes in Arabidopsis thaliana
Degree PhD
Department Biochemistry
Advisory Committee
Advisor Name Title
Gillaspy, Glenda E. Committee Chair
Beers, Eric P. Committee Member
Klemba, Michael Committee Member
Sobrado, Pablo Committee Member
Keywords
  • L-histidinol 1-phosphate phosphatase
  • L-histidinol
  • L-histidine
  • inositol monophosphatase
  • inositol
  • Arabidopsis thaliana
Date of Defense 2012-06-11
Availability unrestricted
Abstract
myo-Inositol synthesis and catabolism are crucial in many multicellular eukaryotes for production of phosphatidylinositol and inositol phosphate signaling molecules. myo-inositol monophosphatase (IMP) is a major enzyme required for the synthesis of myo-inositol and breakdown of inositol (1,4,5)-trisphosphate (InsP3), a potent second messenger involved in many biological activities. Arabidopsis contains a single canonical IMP gene, which was previously shown in our lab to encode a bifuntional enzyme with both IMP and L-galactose 1-phosphatase activity. Analysis of metabolite levels in imp mutants showed only slight modifications with less myo-inositol and ascorbate accumulation in these mutants. This result suggests the presence of other functional IMP enzymes in plants. Two other genes in Arabidopsis encode chloroplast proteins, which we have classified as IMP-like (IMPL), because of their greater homology to the prokaryotic IMPs such as the SuhB, and CysQ proteins. Prokaryotic IMP enzymes are known to dephosphorylate D-Inositol 1-P (D-Ins 1-P) and other substrates in vitro, however their in vivo substrates are not characterized. A recent study revealed the ability of IMPL2 to complement a bacterial histidinol 1-phosphate phosphatase mutant defective in histidine synthesis, which suggested an important role for IMPL2 in amino acid synthesis. The research presented here focuses on the characterization of IMPL functional roles in plant growth and development. To accomplish this I performed kinetic comparisons of the Arabidopsis recombinant IMPL1 and IMPL2 enzymes with various inositol phosphate substrates and with L-histidinol 1-phosphate, respectively. The data supports that IMPL2 gene encodes an active histidinol 1-phosphate phosphatase enzyme in contrast to the IMPL1 enzyme which has the ability to hydrolyze D-Ins 1-P substrate and may be involved in the recycling of inositol from the second messenger, InsP3. Analysis of metabolite levels in impl2 mutant plants reveals that impl2 mutant growth is impacted by alterations in the histidine biosynthesis pathway. Together these data solidify the catalytic role of IMPL2 in histidine synthesis in plants and highlight its importance in plant growth and development.

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