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Structural basis for the activation of human procaspase-7
S J Riedl1, P Fuentes-Prior, M Renatus
1Abteilung Strukturforschung, Max-Planck-Institut für Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany. riedl@biochem.mpg.de
Abstract:
Caspases form a family of proteinases required for the initiation and execution phases of apoptosis. Distinct proapoptotic stimuli lead to activation of the initiator caspases-8 and -9, which in turn activate the common executioner caspases-3 and -7 by proteolytic cleavage. Whereas crystal structures of several active caspases have been reported, no three-dimensional structure of an uncleaved caspase zymogen is available so far. We have determined the 2.9-A crystal structure of recombinant human C285A procaspase-7 and have elucidated the activation mechanism of caspases. The overall fold of the homodimeric procaspase-7 resembles that of the active tetrameric caspase-7. Each monomer is organized in two structured subdomains connected by partially flexible linkers, which asymmetrically occupy and block the central cavity, a typical feature of active caspases. This blockage is incompatible with a functional substrate binding site/active site. After proteolytic cleavage within the flexible linkers, the newly formed chain termini leave the cavity and fold outward to form stable structures. These conformational changes are associated with the formation of an intact active-site cleft. Therefore, this mechanism represents a formerly unknown type of proteinase zymogen activation.
Insights
This study reveals the three-dimensional structure of inactive procaspase-7, detailing how its activation mechanism differs from other proteinase zymogens. Understanding caspase activation is key to apoptosis research.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Caspases are crucial proteinases in apoptosis, with initiator caspases activating executioner caspases via proteolytic cleavage.
- While active caspase structures are known, the three-dimensional structure of uncleaved caspase zymogens remained elusive.
Purpose of the Study:
- To determine the crystal structure of recombinant human C285A procaspase-7.
- To elucidate the activation mechanism of caspases at a structural level.
Main Methods:
- Determined the 2.9-Å crystal structure of recombinant human C285A procaspase-7.
- Analyzed the structural differences between procaspase-7 and active caspase-7.
Main Results:
- The homodimeric procaspase-7 structure resembles active tetrameric caspase-7, with flexible linkers blocking the active site cavity.
- Proteolytic cleavage within these linkers allows termini to move, forming a functional active-site cleft.
- This represents a novel mechanism for proteinase zymogen activation.
Conclusions:
- The structural data provides unprecedented insight into the activation mechanism of caspases.
- This finding reveals a previously unknown mode of proteinase zymogen activation, distinct from other known pathways.