Abstract
We investigate ADPglucose hydrolyzing nucleotide pyrophosphatase/phosphodiesterase (NPP) in rice (Oryza sativa L.). An NPP enzyme was purified and characterized from the shoot tissues of rice germinating seeds. It was shown to be glycosylated, since the enzyme protein bound to Con A, stained with periodic acid-Schiff reagent and could be digested by Endo-H. The complete NPP encoding cDNA, designated as OsNPP1, was isolated and characterized. OsNPP1 contains numerous N-glycosylation sites and a cleavable hydrophobic signal sequence that does not match with the N-terminal part of the mature protein. A confocal-fluorescence microscopy of rice cells expressing OsNPP1-GFP revealed that it occurs in the plastidial compartment, which was confirmed by immunocytochemical studies. Endo-H digestibility studies revealed that both OsNPP1 and OsNPP1-GFP occurring in the chloroplast are glycosylated. These data show the occurrence of a traffic route of glycosylated proteins from the endoplasmic reticulum-Golgi system to the chloroplast in higher plants.
