Expression of 1L-Myoinositol-1-Phosphate Synthase in Organelles

• Published in: Plant physiology (Bethesda) 2003-08, Vol.132 (4), p.2240-2247
• Main Authors: LACKEY, Kimberly Helms, POPE, Patricia Marie, JOHNSON, Margaret Dean
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Antibodies; Base Sequence; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Biosynthesis; Cell Fractionation; Cell membranes; Chloroplasts; Chromosomes; Enzymes; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Immunoblotting; Immunohistochemistry; Inositol phosphates; Inositols; Isoenzymes - genetics; Isoenzymes - metabolism; Metabolism; Mitochondria; Molecular Sequence Data; Organelles; Organelles - enzymology; Phaseolus - cytology; Phaseolus - enzymology; Phaseolus - genetics; Phosphoric Monoester Hydrolases - genetics; Phosphoric Monoester Hydrolases - metabolism; Plant physiology and development; RNA, Messenger - genetics; RNA, Messenger - metabolism; Solubility
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.103.020610

We have studied the expression of 1L-myoinositol-1-phosphate synthase (MIPS; EC 5.5.1.4) in developing organs of Phaseolus vulgaris to define genetic controls that spatially regulate inositol phosphate biosynthesis. MIPS, the pivotal biosynthetic enzyme in inositol metabolism, is the only enzyme known to catalyze the conversion of glucose 6-phosphate to inositol phosphate. It is found in unicellular and multicellular eukaryotes and has been isolated as a soluble enzyme from both. Thus, it is widely accepted that inositol phosphate biosynthesis is largely restricted to the cytosol. Here, we report findings that suggest the enzyme is also expressed in membrane-bound organelles. Microscopic and biochemical analyses detected MIPS expression in plasma membranes, plastids, mitochondria, endoplasmic reticula, nuclei, and cell walls of bean. To address mechanisms by which the enzyme could be targeted to or through membranes, MIPS genes were analyzed for sorting signals within primary structures and upstream open reading frames that we discovered through our sequence analyses. Comprehensive computer analyses revealed putative transit peptides that are predicted to target the enzyme to different cellular compartments. Reverse transcriptase PCR experiments suggest that these putative targeting peptides are expressed in bean roots and leaves.