title: Extensive post-translational processing of potato tuber storage proteins and vacuolar targeting.
abstract: Potato tuber storage proteins were obtained from vacuoles isolated from field-grown starch potato tubers cv. Kuras. Vacuole sap proteins fractionated by gel filtration were studied by mass spectrometric analyses of trypsin and chymotrypsin digestions. The tuber vacuole appears to be a typical protein storage vacuole absent of proteolytic and glycolytic enzymes. The major soluble storage proteins included 28 Kunitz protease inhibitors, nine protease inhibitors 1, eight protease inhibitors 2, two carboxypeptidase inhibitors, eight patatins and five lipoxygenases (lox), which all showed cultivar-specific sequence variations. These proteins, except for lox, have typical endoplasmic reticulum (ER) signal peptides and putative vacuolar sorting determinants of either the sequence or structure specific type or the C-terminal type, or both. Unexpectedly, sap protein variants imported via the ER showed multiple molecular forms because of extensive and unspecific proteolytic cleavage of exposed N- and C-terminal propeptides and surface loops, in spite of the abundance of protease inhibitors. Some propeptides are potential novel vacuolar targeting peptides. In the insoluble vacuole fraction two variants of phytepsin (aspartate protease) were identified. These are most probably the processing enzymes of potato tuber vacuolar proteins. Database Proteome data have been submitted to the PRIDE database under accession number 17707.
authors.affiliation: Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Aalborg, Denmark.
authors.forename: Malene
authors.initials: M
authors.lastname: Jørgensen
authors.forename: Allan
authors.initials: A
authors.lastname: Stensballe
authors.forename: Karen Gjesing
authors.initials: KG
authors.lastname: Welinder
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000378:metabolism; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D020543:Proteome; D017386:Sequence Homology, Amino Acid; D011198:Solanum tuberosum / Q000201:enzymology / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D020543:Proteome