title: Molecular control of phenoloxidase-induced melanin synthesis in an insect.
abstract: The melanization reaction induced by activated phenoloxidase in arthropods must be tightly controlled because of excessive formation of quinones and excessive systemic melanization damage to the hosts. However, the molecular mechanism by which phenoloxidase-induced melanin synthesis is regulated in vivo is largely unknown. It is known that the Spätzle-processing enzyme is a key enzyme in the production of cleaved Spätzle from pro-Spätzle in the Drosophila Toll pathway. Here, we provide biochemical evidence that the Tenebrio molitor Spätzle-processing enzyme converts both the 79-kDa Tenebrio prophenoloxidase and Tenebrio clip-domain SPH1 zymogen to an active melanization complex. This complex, consisting of the 76-kDa Tenebrio phenoloxidase and an active form of Tenebrio clip-domain SPH1, efficiently produces melanin on the surface of bacteria, and this activity has a strong bactericidal effect. Interestingly, we found the phenoloxidase-induced melanization reaction to be tightly regulated by Tenebrio prophenoloxidase, which functions as a competitive inhibitor of melanization complex formation. These results demonstrate that the Tenebrio Toll pathway and the melanization reaction share a common serine protease for the regulation of these two major innate immune responses.
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea; School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang 110016, China.
authors.forename: Hongnan
authors.initials: H
authors.lastname: Kan
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
authors.forename: Chan-Hee
authors.initials: CH
authors.lastname: Kim
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
authors.forename: Hyun-Mi
authors.initials: HM
authors.lastname: Kwon
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
authors.forename: Ji-Won
authors.initials: JW
authors.lastname: Park
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
authors.forename: Kyung-Baeg
authors.initials: KB
authors.lastname: Roh
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
authors.forename: Hanna
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Molecular Biology, College of Natural Science, Pusan National University, Busan 609-735, Korea.
authors.forename: Bum-Joon
authors.initials: BJ
authors.lastname: Park
authors.affiliation: School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang 110016, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.affiliation: School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang 110016, China.
authors.forename: Jinghai
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Comparative Physiology, Evolutionary Biology Center, Uppsala University, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Söderhäll
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
authors.forename: Nam-Chul
authors.initials: NC
authors.lastname: Ha
authors.affiliation: National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea. Electronic address: brlee@pusan.ac.kr.
authors.forename: Bok Luel
authors.initials: BL
authors.lastname: Lee
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology; D001419:Bacteria / Q000378:metabolism; D004330:Drosophila / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D007113:Immunity, Innate; D019476:Insect Proteins / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008543:Melanins / Q000096:biosynthesis* / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D014442:Monophenol Monooxygenase / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D013712:Tenebrio
chemical_list: D000890:Anti-Infective Agents; D019476:Insect Proteins; D008543:Melanins; D010455:Peptides; D011994:Recombinant Proteins; D014442:Monophenol Monooxygenase; D008239:Lysine