Abstract
Antimicrobial peptides (AMPs) are key components of innate immunity and are widespread in nature, from bacteria to vertebrate animals. In crustaceans, there are currently 15 distinct AMP families published so far in the literature, mainly isolated from members of the Decapoda order. Up to now, armadillidin is the sole non-decapod AMP isolated from the haemocytes of Armadillidium vulgare, a crustacean isopod. Its first description demonstrated that armadillidin is a linear glycine-rich (47%) cationic peptide with an antimicrobial activity directed toward Bacillus megaterium. In the present work, we report identification of armadillidin Q, a variant of armadillidin H (earlier known as armadillidin), from crude haemocyte extracts of A. vulgare using LC-MS approach. We demonstrated that both armadillidins displayed broad spectrum antimicrobial activity against several Gram-positive and Gram-negative bacteria, fungi, but were totally inactive against yeasts. Membrane permeabilization assays, only performed with armadillidin H, showed that the peptide is membrane active against bacterial and fungal strains leading to deep changes in cell morphology. This damaging activity visualized by electronic microscopy correlates with a rapid decrease of cell viability leading to highly blebbed cells. In contrast, armadillidin H does not reveal cytotoxicity toward human erythrocytes. Furthermore, no secondary structure could be defined in this study [by circular dichroism (CD) and nuclear magnetic resonance (NMR)] even in a membrane mimicking environment. Therefore, armadillidins represent interesting candidates to gain insight into the biology of glycine-rich AMPs.
Highlights
By their number and their diversity, arthropods play an essential role in all ecosystems
Discovery of an Armadillidin H Variant in Haemocytes of Armadillidium vulgare To find out if armadillidin is the only Antimicrobial peptides (AMPs) produced and stored in A. vulgare haemocytes (Herbiniere et al, 2005), a crude extract prepared from haemocytes of 100 animals was analyzed by LC-MS
Results showed the presence of two variants of armadillidin encoded in the genome of A. vulgare, the second one differing from the previously described one (Herbiniere et al, 2005) by only one amino acid substitution: a H is replaced by a Q at position 33
Summary
By their number and their diversity, arthropods play an essential role in all ecosystems They are widely distributed and can exploit a very diverse range of niches in both terrestrial and aquatic environments. Terrestrial crustacean species are perfectly adapted to the life out of water, notably the terrestrial isopods which constitute an important component of the soil fauna (Jeffery et al, 2010; Hornung, 2011). As they break down more than 10% of the decaying leaf litter of many plant species (Curry, 1987), terrestrial isopods are classified as detritivorous. They are in permanent contact with abundant and diverse communities of microorganisms (Jeffery et al, 2010)
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