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AIP56: A Novel Bacterial Apoptogenic Toxin

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Author(s): Manuel T. Silva | Nuno M. S. dos Santos | Ana do Vale

Journal: Toxins
ISSN 2072-6651

Volume: 2;
Issue: 4;
Start page: 905;
Date: 2010;
Original page

Keywords: Photobacterium damselae subsp. piscicida | AIP56 | AB toxin | apoptosis | secondary necrosis

ABSTRACT
Photobacterium damselae subsp. piscicida (Phdp) is a Gram-negative pathogen agent of an important fish septicemia. The key virulence factor of Phdp is the plasmid-encoded exotoxin AIP56, which is secreted by exponentially growing pathogenic strains. AIP56 has 520 amino acids including an N-terminal cleavable signal peptide of 23 amino acid residues, two cysteine residues and a zinc-binding region signature HEXXH that is typical of most zinc metallopeptidases. AIP56 induces in vitro and in vivo selective apoptosis of fish macrophages and neutrophils through a caspase-3 dependent mechanism that also involves caspase-8 and -9. In vivo, the AIP56-induced phagocyte apoptosis progresses to secondary necrosis with release of cytotoxic phagocyte molecules including neutrophil elastase. Fish injected with recombinant AIP56 die with a pathology similar to that seen in the natural infection.
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