TERRAPUB Aqua-BioScience Monographs


Vol. 8 (No. 1), pp. 1–26, 2015 doi:10.5047/absm.2015.00801.0001

L-Amino Acid Oxidase, a Novel Antibacterial Protein in the Rockfish Sebastes schlegeli

Yoichiro Kitani, Shoichiro Ishizaki and Yuji Nagashima*

Department of Food Science and Technology
Graduate School of Marine Science and Technology
Tokyo University of Marine Science and Technology
4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan
*e-mail: yujicd@kaiyodai.ac.jp

(Received on April 12, 2014; Accepted on August 4, 2014; Online published on October 26, 2015)

Abstract: Fish have elaborate humoral factors in their nonspecific defense mechanisms and skin mucus covering their surface contains a variety of antibacterial proteins and peptides. Since we first identified L-amino acid oxidase (LAO) as an antibacterial protein (SSAP; Sebastes shlegeli antibacterial protein) in the rockfish S. shlegeli skin mucus, LAO was recognized as a novel type of antibacterial agent in fish. SSAP, antibacterial LAO, is a glycoprotein with a molecular mass of 120 kDa and a homodimer consisting of a 53 kDa subunit. SSAP was determined to contain FAD as a coenzyme and have the strict substrate specificity to L-lysine. It potently and selectively showed antibacterial activity against water-borne Gram-negative pathogens such as Aeromonas hydrophila, Aeromonas salmonicida, Photobacterium damselae subsp. piscicida and Vibrio parahaemolyticus by production of hydrogen peroxide. Electron microscopic analysis revealed that SSAP damaged the bacteria in different manners. SSAP was predominantly synthesized in skin and gill. SSAP mRNA positive cells were observed near the basal membrane of skin epidermis and the gill epithelium by in situ hybridization. Another LAO with antibacterial activity was isolated in serum of the rockfish. These results suggest that antibacterial LAOs are deeply involved in innate immunity of the rockfish.

Keywords: L-amino acid oxidase, antibacterial protein, skin mucus, rockfish Sebastes schlegeli, innate immunity


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