IMR Press / FBL / Volume 12 / Issue 9 / DOI: 10.2741/2317

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on as a courtesy and upon agreement with Frontiers in Bioscience.

Open Access Article
Regulation of caspase-9 activity by differential binding to the apoptosome complex
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1 Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
Academic Editor:Pudur Jagadeeswaran
Front. Biosci. (Landmark Ed) 2007, 12(9), 3343–3354;
Published: 1 May 2007
(This article belongs to the Special Issue The zebrafish as a model for human disease)

Proteolytic processing of procaspase-9 is required for its activation, but processing in itself appears to be insufficient for its activity. We studied caspase activation in a cell-free system and found that incubation of cytosol from rat kidney proximal tubule cells with Cytochrome c (Cyt c) and dATP results in rapid autocatalytic processing of procaspase-9 from ~50 kD to ~38 kD size fragment. Moreover, Cyt c concentration influences the production of alternatively processed forms of caspase-9. At lower Cyt c concentration (0.01-0.05 mg/ml), two fragments of caspase-9 of the size 38 and 40 kD are produced. In contrast, at higher concentrations of Cyt c (>0.1 mg/ml) only 38 kD fragment will prevail. However, our failure to capture processed caspase-9 by affinity labeling or co-elution with Apaf-1 suggested that caspase-9 undergoes a conformational change during its enzymatic action on effector caspases, resulting in its release from the apoptosome complex and inactivation. In support of this hypothesis, catalytic inhibitors of caspase-9 prevented its release from the apoptosome complex without affecting its auto-processing and allowed successful capture of active caspase-9 (38 kD) and its complex by affinity labeling. These observations suggest that complex allosteric interactions with the apoptosome complex influence caspase-9 activity and function by controlling not only the induction of its enzymatic activity, but also its rapid termination.

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