title: Plastidial starch phosphorylase in sweet potato roots is proteolytically modified by protein-protein interaction with the 20S proteasome.
abstract: Post-translational regulation plays an important role in cellular metabolism. Earlier studies showed that the activity of plastidial starch phosphorylase (Pho1) may be regulated by proteolytic modification. During the purification of Pho1 from sweet potato roots, we observed an unknown high molecular weight complex (HX) showing Pho1 activity. The two-dimensional gel electrophoresis, mass spectrometry, and reverse immunoprecipitation analyses showed that HX is composed of Pho1 and the 20S proteasome. Incubating sweet potato roots at 45°C triggers a stepwise degradation of Pho1; however, the degradation process can be partially inhibited by specific proteasome inhibitor MG132. The proteolytically modified Pho1 displays a lower binding affinity toward glucose 1-phosphate and a reduced starch-synthesizing activity. This study suggests that the 20S proteasome interacts with Pho1 and is involved in the regulation of the catalytic activity of Pho1 in sweet potato roots under heat stress conditions.
authors.affiliation: Department of Biochemical Science and Technology, and Institute of Microbiology and Biochemistry, National Taiwan University, Taipei, Taiwan.
authors.forename: Yi-Chen
authors.initials: YC
authors.lastname: Lin
authors.forename: Han-Min
authors.initials: HM
authors.lastname: Chen
authors.forename: I-Min
authors.initials: IM
authors.lastname: Chou
authors.forename: An-Na
authors.initials: AN
authors.lastname: Chen
authors.forename: Chia-Pei
authors.initials: CP
authors.lastname: Chen
authors.forename: Guang-Huar
authors.initials: GH
authors.lastname: Young
authors.forename: Chi-Tsai
authors.initials: CT
authors.lastname: Lin
authors.forename: Chiung-Hsiang
authors.initials: CH
authors.lastname: Cheng
authors.forename: Shih-Chung
authors.initials: SC
authors.lastname: Chang
authors.forename: Rong-Huay
authors.initials: RH
authors.lastname: Juang
mesh_terms: D002384:Catalysis; D027723:Ipomoea batatas / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D024941:Starch Phosphorylase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D024941:Starch Phosphorylase; D046988:Proteasome Endopeptidase Complex