Plastidial starch phosphorylase in sweet potato roots is proteolytically modified by protein-protein interaction with the 20S proteasome

• Published in: PloS one 2012-04, Vol.7 (4), p.e35336-e35336
• Main Authors: Lin, Yi-Chen, Chen, Han-Min, Chou, I-Min, Chen, An-Na, Chen, Chia-Pei, Young, Guang-Huar, Lin, Chi-Tsai, Cheng, Chiung-Hsiang, Chang, Shih-Chung, Juang, Rong-Huay
• Format: Article
• Language: English
• Subjects: Amino acids; Analysis; Biochemistry; Biology; Biosynthesis; Catalysis; Catalytic activity; Cell cycle; Degradation; Dehydrogenases; Enzymes; Gel electrophoresis; Glucose; Handbooks; Heat stress; Heat tolerance; Immunoprecipitation; Ipomoea batatas - chemistry; Ipomoea batatas - enzymology; Ipomoea batatas - metabolism; Mass spectrometry; Mass spectroscopy; Metabolism; Molecular weight; Oxidative stress; Phosphorylation; Physiological aspects; Plant Roots - chemistry; Plant Roots - metabolism; Post-translation; Potatoes; Proteasome Endopeptidase Complex - chemistry; Proteasome Endopeptidase Complex - isolation & purification; Proteasome Endopeptidase Complex - metabolism; Proteasome inhibitors; Protein interaction; Protein Interaction Domains and Motifs; Protein Structure, Tertiary; Protein-protein interactions; Proteins; Proteolysis; Roots; Starch; Starch phosphorylase; Starch Phosphorylase - chemistry; Starch Phosphorylase - isolation & purification; Starch Phosphorylase - metabolism; Sweet potatoes; Vegetables; Veterinary medicine
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0035336

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.