title: Sweet potato cysteine proteases SPAE and SPCP2 participate in sporamin degradation during storage root sprouting.
abstract: Sweet potato sporamins are trypsin inhibitors and exhibit strong resistance to digestion by pepsin, trypsin and chymotrypsin. In addition, they constitute the major storage proteins in the sweet potato and, after degradation, provide nitrogen as a nutrient for seedling regrowth in sprouting storage roots. In this report, four cysteine proteases-one asparaginyl endopeptidase (SPAE), two papain-like cysteine proteases (SPCP1 and SPCP2), and one granulin-containing cysteine protease (SPCP3)-were studied to determine their association with sporamin degradation in sprouting storage roots. Sporamin degradation became significant in the flesh of storage roots starting from week 4 after sprouting and this correlated with expression levels of SPAE and SPCP2, but not of SPCP1 and SPCP3. In the outer flesh near the skin, sporamin degradation was more evident and occurred earlier than in the inner flesh of storage roots. Degradation of sporamins in the outer flesh was inversely correlated with the distance of the storage root from the sprout. Exogenous application of SPAE and SPCP2, but not SPCP3, fusion proteins to crude extracts of the outer flesh (i.e., extracted from a depth of 0.3cm and within 2cm of one-week-old sprouts) promoted in vitro sporamin degradation in a dose-dependent manner. Pre-treatment of SPAE and SPCP2 fusion proteins at 95°C for 5min prior to their application to the crude extracts reduced sporamin degradation. These data show that sweet potato asparaginyl endopeptidase SPAE and papain-like cysteine protease SPCP2 participate in sporamin degradation during storage root sprouting.
authors.affiliation: Department of Biological Sciences, National Sun Yat-sen University, 804 Kaohsiung, Taiwan. Electronic address: hjchen@faculty.nsysu.edu.tw.
authors.forename: Hsien-Jung
authors.initials: HJ
authors.lastname: Chen
authors.affiliation: Department of Biological Sciences, National Sun Yat-sen University, 804 Kaohsiung, Taiwan.
authors.forename: Shu-Hao
authors.initials: SH
authors.lastname: Liang
authors.affiliation: Graduate Institute of Chinese Pharmaceutical Sciences, China Medical University, 404 Taichung, Taiwan.
authors.forename: Guan-Jhong
authors.initials: GJ
authors.lastname: Huang
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, Nankang, 115 Taipei, Taiwan. Electronic address: boyhlin@gate.sinica.edu.tw.
authors.forename: Yaw-Huei
authors.initials: YH
authors.lastname: Lin
mesh_terms: D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D057056:Cysteine Proteases / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D027723:Ipomoea batatas / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D014361:Trypsin Inhibitors / Q000378:metabolism*; D000099240:Asparaginyl Endopeptidase
chemical_list: D003546:Cysteine Endopeptidases; D057056:Cysteine Proteases; D010940:Plant Proteins; D014361:Trypsin Inhibitors; D000099240:Asparaginyl Endopeptidase; C067142:sporamin protein, Ipomoea batatas
keywords: Cysteine protease; Sporamin; Sprout; Sweet potato; Trypsin inhibitor