title: Antimicrobial, dehydroascorbate reductase, and monodehydroascorbate reductase activities of defensin from sweet potato [Ipomoea batatas (L.) Lam. 'Tainong 57'] storage roots.
abstract: A cDNA encoding a small cysteine-rich protein designated defensin (SPD1) was isolated from sweet potato storage roots. On the basis of the amino acid sequence similarity and conserved residues, it is suggested that SPD1 is a member of the plant defensin family. Recombinant SPD1 protein overproduced in Escherichia coli was purified by Ni (2+)-chelated affinity chromatography. A recombinant protein from the storage root cDNA clone effectively inhibited the trypsin activity in a dose-dependent manner. Both the corresponding mRNA and protein level were found to be highest in the storage roots, followed by sprout. SPD1 reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate l-ascorbic acid (AsA). However, without glutathione, SPD1 has very low DHA reductase activity, and AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radical. MDA was also reduced by SPD1 to AsA in the presence of NADH, mimicking the MDA reductase catalyzed reaction. These data suggest that SPD1 has both DHA reductase and MDA reductase activities. SPD1 was also shown to inhibit the growth of both fungi and bacteria. SPD1 is apparently the first reported plant defensin exhibiting DHA and MDA activities in vitro.
authors.affiliation: Institute of Chinese Pharmaceutical Sciences, Department of Physiology, School of Medicine, and School of Pharmacy, China Medical University, Taichung 404, Taiwan.
authors.forename: Guan-Jhong
authors.initials: GJ
authors.lastname: Huang
authors.forename: Hsin-Chih
authors.initials: HC
authors.lastname: Lai
authors.forename: Yuan-Shiun
authors.initials: YS
authors.lastname: Chang
authors.forename: Ming-Jyh
authors.initials: MJ
authors.lastname: Sheu
authors.forename: Te-Ling
authors.initials: TL
authors.lastname: Lu
authors.forename: Shyh-Shyun
authors.initials: SS
authors.lastname: Huang
authors.forename: Yaw-Huei
authors.initials: YH
authors.lastname: Lin
mesh_terms: D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001483:Base Sequence; D018076:DNA, Complementary / Q000737:chemistry; D023082:Defensins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D027723:Ipomoea batatas / Q000737:chemistry*; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry
chemical_list: D000890:Anti-Infective Agents; D018076:DNA, Complementary; D023082:Defensins; D010088:Oxidoreductases; D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH); C020666:glutathione dehydrogenase (ascorbate)