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Target protease specificity of the viral serpin CrmA. Analysis of five caspases
Abstract:
When ectopically expressed in animal cells, cytokine response modifier A (CrmA), a product of the cowpox virus, prevents programmed cell death initiated by a variety of stimuli. Since CrmA is a proteinase inhibitor, its target is probably a protease that promotes cell death. The identification of this target is crucial in delineating essential regulation points that modulate the apoptotic program. We have compared the kinetics of interaction of CrmA with five proteases that may play a role in apoptosis. Four of the proteases, all members of the caspase family, are inhibited with widely different rates and affinities ranging over 5 orders of magnitude. One is not inhibited at all under the experimental conditions. CrmA is quite selective in its ability to inhibit caspases, showing the highest affinity for interleukin-1beta-converting enzyme and the second highest for the caspase FLICE (Ki = 0.95 nM), identified as a component of the intracellular signaling complex recruited by ligation of the death receptor Fas. On the basis of comparative inhibitor kinetics, we propose that CrmA is unlikely to inhibit the caspases Yama, Mch2, or LAP3 in vivo but that its inhibition of FLICE is of a magnitude for this protease to be a key target of CrmA during Fas-mediated apoptosis. Therefore, our results support the hypothesis that FLICE catalyzes a crucial step in the promotion of cell death.
Insights
Cytokine response modifier A (CrmA) from cowpox virus inhibits programmed cell death by targeting specific caspases. Researchers found CrmA strongly inhibits FLICE, a key protease in Fas-mediated apoptosis, supporting its role in cell death regulation.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Cytokine response modifier A (CrmA), a cowpox virus protein, inhibits apoptosis in animal cells.
- CrmA's mechanism involves proteinase inhibition, suggesting a role in targeting cell death-promoting proteases.
- Identifying CrmA's target is crucial for understanding apoptosis regulation.
Purpose of the Study:
- To identify the specific protease target of CrmA involved in apoptosis.
- To compare the interaction kinetics of CrmA with five potential apoptotic proteases.
- To determine if CrmA's inhibition of specific caspases is significant in Fas-mediated apoptosis.
Main Methods:
- Comparative inhibitor kinetics analysis of CrmA against five proteases.
- Assessing the rates and affinities of CrmA interaction with caspase family members.
- Evaluating CrmA's inhibitory activity against interleukin-1beta-converting enzyme, FLICE, Yama, Mch2, and LAP3.
Main Results:
- CrmA exhibited selective inhibition of caspases, with varying rates and affinities across a 5-log range.
- CrmA showed the highest affinity for interleukin-1beta-converting enzyme and the second highest for FLICE (Ki = 0.95 nM).
- CrmA demonstrated minimal to no inhibition of Yama, Mch2, and LAP3 under experimental conditions.
Conclusions:
- CrmA's potent inhibition of FLICE suggests it is a key target in Fas-mediated apoptosis.
- FLICE is proposed to catalyze a critical step in promoting programmed cell death.
- The findings delineate CrmA's specificity and highlight FLICE's central role in apoptotic pathways.