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Potato tuber storage proteins were obtained from vacuoles isolated from field-grown starch potato tubers cv. Kuras. Vacuole sap proteins fraction-ated by gel filtration were studied by mass spectrometric analyses of trypsin and chymotrypsin digestions. | IFEBS Journal Extensive post-translational processing of potato tuber storage proteins and vacuolar targeting Malene J0rgensen Allan Stensballe and Karen Gjesing Welinder Protein Chemistry Group Department of Biotechnology Chemistry and EnvironmentalEngineering Aalborg University Denmark Keywords carboxypeptidase inhibitor Kunitz protease inhibitor lipoxygenase mitochondrial processing protease phytepsin protease inhibitor 1 protease inhibitor 2 Solanum tuberosum vacuolar targeting peptides Correspondence K. G. Welinder Department of Biotechnology Chemistry and Environmental Engineering Aalborg University Sohngaardsholmsvej49 DK-9000 Aalborg Denmark Fax 45 9814 1808 Tel 45 2196 5333 E-mail kgw@bio.aau.dk Present address Department of ClinicalImmunology Aalborg Hospital Aarhus University Hospital DK-9000 Aalborg Denmark Received 1 July 2011 revised 10 August 2011 accepted 16 August 2011 doi 10.1111 j.1742-4658.2011.08311.x 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
