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Involvement of peroxidase in chorion hardening in Aedes aegypti
J Li1, B A Hodgeman, B M Christensen
1Department of Animal Health and Biomedical Sciences, University of Wisconsin-Madison 53706, U.S.A.
Insights
Mosquito egg hardening involves peroxidase activity, peaking after a blood meal. This enzyme catalyzes dityrosine formation, contributing to chorion crosslinking and egg survival.
Area of Science:
- Biochemistry
- Entomology
- Molecular Biology
Background:
- Mosquito eggshell (chorion) hardening is crucial for embryonic survival.
- The enzymatic processes underlying chorion hardening in Aedes aegypti are not fully understood.
Purpose of the Study:
- To investigate the role of peroxidase in Aedes aegypti egg chorion hardening.
- To identify and characterize chorion-associated peroxidases and their substrates.
Main Methods:
- Detection and quantification of peroxidase activity in Aedes aegypti ovaries and eggs post-blood feeding.
- SDS-PAGE analysis of chorion proteins to identify peroxidase and phenol oxidase.
- Biochemical assays to detect dityrosine and trityrosine formation.
Main Results:
- Peroxidase activity was detected in ovaries and mature eggs, peaking 36-48 hours after a blood meal.
- SDS-PAGE confirmed the presence of peroxidase (approx. 61,000 Da) and phenol oxidase in the chorion.
- Tyrosine residues in chorion proteins were crosslinked via dityrosine and trityrosine formation, catalyzed by peroxidase.
Conclusions:
- Chorion peroxidase plays a key role in hardening Aedes aegypti eggs by catalyzing dityrosine crosslinking of structural proteins.
- Egg hardening is a combined process involving peroxidase-mediated crosslinking and phenol oxidase-mediated melanization.
Abstract:
Peroxidase activity is detectable in Aedes aegypti ovaries, containing developing eggs, at 24 h following blood feeding, and peak peroxidase activity is reached at 36-48 h after the blood-meal. Peroxidase is associated with the chorion layer in mature eggs and the majority of the enzyme is released from the chorion layer by treating the isolated chorion fraction with SDS/urea. Analysis of the SDS/urea solubilized chorion proteins using SDS-PAGE with tropolone/H2O2 or dopa staining verified the presence of both peroxidase and phenol oxidase in the released chorion proteins. The molecular weight of chorion peroxidase is about 61,000 Da as determined by SDS-PAGE analysis. Incubation of the solubilized chorion proteins with tyrosine and H2O2 produces dityrosine, and hyrolysis of hardened egg chorion results in the detection of dityrosine and trityrosine in the chorion hydrolysate. Data suggest that chorion peroxidase is involved in the hardening of the mosquito egg chorion by catalyzing the formation of ditryrosine through tyrosine residues on structural proteins. The overall hardening of the A. aegypti egg chorion includes both peroxidase-mediated chorion protein crosslinking through dityrosine formation and phenol oxidase-catalyzed chorion melanization.