Plancitoxins, lethal factors from the crown-of-thorns starfish Acanthaster planci, are deoxyribonucleases II

Area of Science:

• Marine biology
• Biochemistry
• Toxicology

Background:

• The crown-of-thorns starfish (Acanthaster planci) possesses potent toxins in its spines.
• Understanding these toxins is crucial for marine toxicology and potential biomedical applications.

Purpose of the Study:

• To purify and characterize lethal toxins from Acanthaster planci spines.
• To elucidate the molecular structure and enzymatic activity of these toxins.
• To identify potential homologs and functional similarities with known enzymes.

Main Methods:

• Purification of plancitoxins I and II using biochemical techniques.
• Assessment of hepatotoxicity through serum enzyme level analysis (glutamic oxaloacetic transaminase, glutamic pyruvic transaminase).
• Structural analysis using SDS-PAGE and N-terminal amino acid sequencing.
• cDNA cloning via RT-PCR, 3'-RACE, and 5'-RACE.
• Enzymatic activity assay for DNA degradation.

Main Results:

• Two lethal toxins, plancitoxins I and II, were purified with an LD50 of 140 microg/kg.
• Both toxins demonstrated potent hepatotoxicity in mice.
• Plancitoxins consist of alpha (10 kDa) and beta (27 kDa) subunits linked by disulfide bonds.
• The cDNA encoding plancitoxin I was cloned, revealing subunits coded in order.
• Plancitoxin I shares 40-42% homology with mammalian deoxyribonucleases II (DNases II) and exhibits DNA degrading activity at pH 7.2.

Conclusions:

• Plancitoxins I and II are potent hepatotoxins derived from Acanthaster planci.
• Plancitoxin I represents the first identified toxic deoxyribonuclease II (DNase II).
• The structural elucidation and enzymatic activity of plancitoxin I offer insights into toxin evolution and function.