Antimicrobial peptides in echinoderm host defense

• Echinoderms and their immunity are addressed.
• The fundamental characters of antimicrobial peptides (AMPs) and their mechanisms of antimicrobial activity are summarized.
• How AMPs enable innate immune response modulation is discussed.
• Two well-characterized AMP families in Strongylocentrotus droebachiensis, strongylocins and centrocins, are described.
• Other AMPs from echinoderms, including beta-thymosin, the lectin fragment CEL-III, and holothuroidins are included.

Antimicrobial peptides (AMPs) are important effector molecules in innate immunity. Here we briefly summarize characteristic traits of AMPs and their mechanisms of antimicrobial activity. Echinoderms live in a microbe-rich marine environment and are known to express a wide range of AMPs. We address two novel AMP families from coelomocytes of sea urchins: cysteine-rich AMPs (strongylocins) and heterodimeric AMPs (centrocins). These peptide families have conserved preprosequences, are present in both adults and pluteus stage larvae, have potent antimicrobial properties, and therefore appear to be important innate immune effectors. Strongylocins have a unique cysteine pattern compared to other cysteine-rich peptides, which suggests a novel AMP folding pattern. Centrocins and SdStrongylocin 2 contain brominated tryptophan residues in their native form. This review also includes AMPs isolated from other echinoderms, such as holothuroidins, fragments of beta-thymosin, and fragments of lectin (CEL-III). Echinoderm AMPs are crucial molecules for the understanding of echinoderm immunity, and their potent antimicrobial activity makes them potential precursors of novel drug leads.