title: Identification of an antibacterial protein as L-amino acid oxidase in the skin mucus of rockfish Sebastes schlegeli.
abstract: Fish skin mucus contains a variety of antimicrobial proteins and peptides that seem to play a role in self defense. We previously reported an antibacterial protein in the skin secretion of the rockfish, Sebastes schlegeli, which showed selective antibacterial activity against Gram-negative bacteria. This study aimed to isolate and structurally and functionally characterize this protein. The antibacterial protein, termed SSAP (S. schlegeli antibacterial protein), was purified to homogeneity by lectin affinity column chromatography, anion-exchange HPLC and hydroxyapatite HPLC. It was found to be a glycoprotein containing N-linked glycochains and FAD. Its molecular mass was estimated to be 120 kDa by gel filtration HPLC and 53 kDa by SDS/PAGE, suggesting that it is a homodimer. On the basis of the partial amino-acid sequence determined, a full-length cDNA of 2037 bp including an ORF of 1662 bp that encodes 554 amino-acid residues was cloned by 3' RACE, 5' RACE and RT-PCR. A blast search showed that a mature protein (496 residues) is homologous to l-amino acid oxidase (LAO) family proteins. SSAP was determined to have LAO activity by the H(2)O(2)-generation assay and substrate specificity for only l-Lys with a K(m) of 0.19 mm. It showed potent antibacterial activity against fish pathogens such as Aeromonas hydrophila, Aeromonas salmonicida and Photobacterium damselae ssp. piscicida. The antibacterial activity was completely lost on the addition of catalase, confirming that H(2)O(2) is responsible for the growth inhibition. This study identifies SSAP as a new member of the LAO family and reveals LAO involvement in the innate immunity of fish skin.
authors.affiliation: Department of Food Science and Technology, Tokyo University of Marine Science and Technology, Japan.
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Kitani
authors.forename: Chihiro
authors.initials: C
authors.lastname: Tsukamoto
authors.forename: Guohua
authors.initials: G
authors.lastname: Zhang
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nagai
authors.forename: Masami
authors.initials: M
authors.lastname: Ishida
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Ishizaki
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Shimakura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shiomi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nagashima
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005399:Fishes / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D050830:L-Amino Acid Oxidase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009093:Mucus / Q000201:enzymology*; D016415:Sequence Alignment; D012867:Skin / Q000201:enzymology* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D018076:DNA, Complementary; D006861:Hydrogen Peroxide; D050830:L-Amino Acid Oxidase; D008239:Lysine