Javad Torabinejad

TL;DR: MIPS1 has a significant impact on myo-inositol levels that is critical for maintaining levels of ascorbic acid, phosphatidyl inositol, and ceramides that regulate growth, development, and cell death.

Abstract: Myoinositol synthesis and catabolism are crucial in many multiceullar eukaryotes for the production of phosphatidylinositol signaling molecules, glycerophosphoinositide membrane anchors, cell wall pectic noncellulosic polysaccharides, and several other molecules including ascorbate. Myoinositol monophosphatase (IMP) is a major enzyme required for the synthesis of myoinositol and the breakdown of myoinositol (1,4,5)trisphosphate, a potent second messenger involved in many biological activities. It has been shown that the VTC4 enzyme from kiwifruit (Actinidia deliciosa) has similarity to IMP and can hydrolyze l-galactose 1-phosphate (l-Gal 1-P), suggesting that this enzyme may be bifunctional and linked with two potential pathways of plant ascorbate synthesis. We describe here the kinetic comparison of the Arabidopsis (Arabidopsis thaliana) recombinant VTC4 with d-myoinositol 3-phosphate (d-Ins 3-P) and l-Gal 1-P. Purified VTC4 has only a small difference in the Vmax/Km for l-Gal 1-P as compared with d-Ins 3-P and can utilize other related substrates. Inhibition by either Ca2+ or Li+, known to disrupt cell signaling, was the same with both l-Gal 1-P and d-Ins 3-P. To determine whether the VTC4 gene impacts myoinositol synthesis in Arabidopsis, we isolated T-DNA knockout lines of VTC4 that exhibit small perturbations in abscisic acid, salt, and cold responses. Analysis of metabolite levels in vtc4 mutants showed that less myoinositol and ascorbate accumulate in these mutants. Therefore, VTC4 is a bifunctional enzyme that impacts both myoinositol and ascorbate synthesis pathways.

TL;DR: Biochemical analyses of a subgroup of 5PTase enzymes suggest that these enzymes have both overlapping and unique substrate preferences and that regulation of Ins(1,4,5)P3 levels is important during germination and early seedling development.

TL;DR: Inositol is required for many cellular processes, especially in eukaryotes, and inositol phosphates that function in signal transduction pathways in yeast and animal cells, are primarily incorporated into phosphatidylinositol (PI)s, and myoinositol monophosphatase (IMPase), which catalyzes the reaction catalyzed by MIPS.

TL;DR: This work characterized two T-DNA mutants in the At5PTase11 gene, and complemented this mutant, and found that dark-grown 5ptase11 mutants contain increases in inositol (1,4,5) trisphosphate and an inositl bisphosphates that is not a substrate for recombinant 5PTase 11.