Involvement of pro-phenoloxidase 3 in lamellocyte-mediated spontaneous melanization in Drosophila.
Phenoloxidase (PO), a melanin-forming enzyme around the foreign bodies, is an important component of the host defense system in invertebrates. Pro-PO is the enzymatically inactive zymogen form of PO. In the Drosophila genome, three Pro-PO isoforms have been identified to date. These include Pro-PO1 and 2, which are primarily expressed in crystal cells, and Pro-PO3, which is predominantly found in the lamellocytes. In this study, we demonstrated that Drosophila Pro-PO3, but not Pro-PO1 or 2, is enzymatically active in its zymogen form. These findings were evidenced by spectacular melanin forming capacities of various cells and tissues that overexpressed these proenzymes. Furthermore, the melanization phenotype observed in the lamellocyte-enriched hop(Tum-1) mutant was drastically reduced in the absence of PPO3, indicating that PPO3 plays a major role in the lamellocyte-mediated spontaneous melanization process. Taken together, these findings indicate that the biochemical properties, activation mode and in vivo role of Pro-PO3 are likely distinct from those of the other two Pro-PO enzymes involved in Drosophila physiology.
Division of Life and Pharmaceutical Science, Department of Life Science, Ewha Womans University, Seoul 120-750, Korea.
Hyuck-Jin
HJ
Nam
In-Hwan
IH
Jang
Tsunaki
T
Asano
Won-Jae
WJ
Lee
D000818:Animals; D004156:Catechol Oxidase / Q000378:metabolism*; D004330:Drosophila / Q000201:enzymology; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D006434:Hemocytes / Q000502:physiology*; D008543:Melanins / Q000378:metabolism*
D004792:Enzyme Precursors; D008543:Melanins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase