During stress-induced apoptosis, the initiator caspase-9 is activated by the Apaf-1 apoptosome and must remain bound in order to retain significant catalytic activity. Nevertheless, in apoptotic cells, the vast majority of processed caspase-9 is paradoxically observed outside of the complex. We demonstrate herein that apoptosome-mediated cleavage of procaspase-9 occurs exclusively through a CARD-displacement mechanism, so that unlike the effector procaspase-3, procaspase-9 cannot be processed by the apoptosome as a typical substrate. Indeed, procaspase-9 possessed higher affinity for the apoptosome and could displace processed caspase-9 from the complex, thereby facilitating a continuous cycle of procaspase-9 recruitment/activation, processing, and release from the complex. Due to its rapid autocatalytic cleavage, however, procaspase-9 per se contributed little to the activation of procaspase-3. Thus, the Apaf-1 apoptosome functions as a proteolytic-based “molecular timer”, wherein the intracellular concentration of procaspase-9 sets the overall duration of the timer, procaspase-9 autoprocessing activates the timer, and the rate at which processed caspase-9 dissociates from the complex (and thus loses its capacity to activate procaspase-3) dictates how fast the timer “ticks” over. To understand the physiological relevance of molecular timer in vivo, we are currently generating caspase-9 knock-in mouse models. These mouse models will enhance our understanding of the importance of caspase-9 processing within the apoptosome. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2010-05-791 |
| Date | 21 September 2010 |
| Creators | Malladi, Srinivas |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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