Molecular control of phenoloxidase-induced melanin synthesis in an insect.
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.
Kan
Hongnan
H
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.
Kim
Chan-Hee
CH
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
Kwon
Hyun-Mi
HM
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
Park
Ji-Won
JW
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
Roh
Kyung-Baeg
KB
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
Lee
Hanna
H
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
Park
Bum-Joon
BJ
Department of Molecular Biology, College of Natural Science, Pusan National University, Busan 609-735, Korea.
Zhang
Rong
R
School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang 110016, China.
Zhang
Jinghai
J
School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang 110016, China.
Söderhäll
Kenneth
K
Department of Comparative Physiology, Evolutionary Biology Center, Uppsala University, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
Ha
Nam-Chul
NC
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea.
Lee
Bok Luel
BL
National Research Laboratory of Defense Proteins, College of Pharmacy, Busan 609-735, Korea. Electronic address: brlee@pusan.ac.kr.
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
D000890:Anti-Infective Agents; D019476:Insect Proteins; D008543:Melanins; D010455:Peptides; D011994:Recombinant Proteins; D014442:Monophenol Monooxygenase; D008239:Lysine