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Full sequence and characterization of two insect defensins: immune peptides from the mosquito Aedes aegypti
R Chalk1, C M Albuquerque, P J Ham
1Department of Biological Sciences, Keele University, Staffordshire, U.K.
Abstract:
We report the complete amino acid sequence and biological activity of two immune peptides, from the yellow fever mosquito Aedes aegypti, that are induced in response to infection. Both peptides display biological activity against the Gram positive microbe Micrococcus luteus and substantial sequence homology to insect defensins, small heat-stable, antibiotic peptides previously described from several non-vector insects. These mosquito peptides, designated Ae. aegypti defensins A and B, are isoforms. Defensin B is the most abundant antibacterial peptide in this species whereas defensin A is much less abundant and carries two amino acid substitutions compared to defensin B, making it more basic in character. Apparent convergence between isoforms from Ae. aegypti and the fleshfly Phormia terranovae is discussed. The synergistic activity previously described between Ae. aegypti immune haemolymph and lysozyme is not caused by these peptides because synergy occurred only at concentrations far outside the physiological range seen in Ae. aegypti.
Insights
Two immune peptides, Aedes aegypti defensins A and B, were identified in mosquitoes. These insect defensins show antimicrobial activity against Micrococcus luteus, with Defensin B being more abundant.
Area of Science:
- Immunology
- Molecular Biology
- Entomology
Background:
- Mosquitoes like Aedes aegypti possess innate immune systems to combat infections.
- Insect defensins are small, heat-stable, antibiotic peptides crucial for host defense.
- Understanding mosquito immune peptides is vital for vector control and disease transmission research.
Purpose of the Study:
- To determine the amino acid sequence and biological activity of novel immune peptides from Aedes aegypti.
- To characterize these peptides in relation to known insect defensins.
- To investigate their role in the mosquito's immune response and potential synergistic interactions.
Main Methods:
- Amino acid sequencing of isolated immune peptides.
- In vitro assays to determine antimicrobial activity against Micrococcus luteus.
- Sequence homology analysis with known insect defensins.
- Comparison of peptide abundance and characteristics.
Main Results:
- Complete amino acid sequences for two Aedes aegypti defensins (A and B) were determined.
- Both peptides exhibited antimicrobial activity against the Gram-positive bacterium Micrococcus luteus.
- Defensin B was found to be the predominant isoform, while Defensin A, though less abundant, showed higher basicity due to two amino acid substitutions.
- Sequence homology confirmed their classification as insect defensins.
- These peptides were not responsible for the previously observed synergistic activity between mosquito hemolymph and lysozyme at physiological concentrations.
Conclusions:
- Aedes aegypti defensins A and B are isoforms of insect defensins with demonstrated antimicrobial properties.
- Defensin B is the primary antibacterial peptide in this mosquito species.
- The identified defensins do not account for previously reported synergistic immune effects in Aedes aegypti hemolymph at physiological levels.
- Further research into these mosquito defensins could offer insights into vector immunity and novel antimicrobial strategies.