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The potent mitogen Pasteurella multocida toxin is highly resistant to proteolysis but becomes susceptible at
M G Smyth1, R W Pickersgill, A J Lax
1Institute for Animal Health, Compton, Berkshire, UK.
Abstract:
The susceptibility of the potent mitogen Pasteurella multocida toxin (PMT) to various proteases was investigated. PMT at a toxin to protease molar ratio of 1:1 was resistant to 8 of the 11 proteases tested after one hour. With longer incubation, PMT remained resistant to 7 proteases, and this correlated with a retention of biological activity, indicating that PMT might not require proteolytic cleavage at least until it bound to a cell receptor. Previous evidence had suggested that PMT is processed in the cell via an endosome or lysosome. We have shown that PMT became susceptible to proteolysis when the pH was lowered to 5 or below. This supports the previous suggestion that PMT is processed via a low pH compartment in the cell.
Insights
Pasteurella multocida toxin (PMT) resists proteases, retaining activity until cellular binding. Lowering pH to 5 or below increases PMT susceptibility to proteolysis, supporting its processing in acidic cellular compartments.
Area of Science:
- Microbiology
- Molecular Biology
- Toxicology
Background:
- Pasteurella multocida toxin (PMT) is a potent mitogen.
- Previous studies suggested PMT is processed intracellularly in acidic compartments like endosomes or lysosomes.
Purpose of the Study:
- To investigate the susceptibility of PMT to various proteases.
- To determine the role of pH in PMT proteolysis.
Main Methods:
- PMT was incubated with 11 different proteases at a 1:1 molar ratio.
- Incubation times were varied (1 hour and longer).
- Protease resistance and biological activity were assessed at different pH levels.
Main Results:
- PMT demonstrated resistance to 8 out of 11 proteases after 1-hour incubation.
- PMT remained resistant to 7 proteases with prolonged incubation, retaining biological activity.
- PMT susceptibility to proteolysis significantly increased at pH 5 or below.
Conclusions:
- PMT may not require immediate proteolytic cleavage upon release, potentially needing to bind a cell receptor first.
- The findings support the hypothesis that PMT undergoes processing within low pH cellular compartments.