The epidermolytic toxins are serine proteases

Area of Science:

• Microbiology
• Biochemistry
• Toxicology

Background:

• Strains of Staphylococcus aureus produce epidermolytic toxins (ETA and ETB) responsible for intraepidermal splitting.
• The precise mechanism underlying toxin-induced epidermolysis remains largely unknown despite sequence data availability.

Purpose of the Study:

• To investigate the structural and mechanistic basis of epidermolysis caused by Staphylococcus aureus toxins ETA and ETB.
• To explore potential relationships between these toxins and known protease families.

Main Methods:

• Bioinformatic analysis of ETA and ETB amino acid sequences against the NBRF-PIR database.
• Comparison of toxin sequences with staphylococcal V8 protease and other serine proteases.
• Identification of potential functional domains, such as calcium-binding loops.
• Inhibition assays using ethylenediaminetetraacetic acid (EDTA) in a mouse bioassay.

Main Results:

• ETA and ETB exhibit significant sequence similarity to staphylococcal V8 protease, possessing a conserved catalytic triad.
• The toxins show a distant homology to mammalian serine proteases, primarily around the catalytic triad.
• A putative calcium-binding loop was identified in ETA, suggesting a potential role for calcium.
• ETA-induced epidermolysis in mice was inhibited by EDTA, supporting a calcium-dependent mechanism.

Conclusions:

• Staphylococcus aureus epidermolytic toxins ETA and ETB are structurally related to serine proteases.
• The mechanism of epidermolysis induced by ETA appears to be calcium-dependent.
• Further research is warranted to fully elucidate the enzymatic activity and calcium-binding properties of these toxins.