Caspase-3 Regulatory Mechanisms
From Proteopedia
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Caspase-3 structure [[Image:Casp-3 with subs.png | thumb]] | Caspase-3 structure [[Image:Casp-3 with subs.png | thumb]] | ||
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==== Natural Inhibitors==== | ==== Natural Inhibitors==== | ||
X-linked inhibitor of apoptosis proteins (XIAP) contains the second baculovirus IAP repeat domain (BIR2) targeting caspase-3 and caspase-7. | X-linked inhibitor of apoptosis proteins (XIAP) contains the second baculovirus IAP repeat domain (BIR2) targeting caspase-3 and caspase-7. | ||
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| - | == Importance of Loop Orientation== | ||
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| - | Caspases are extremely dependent on the orientation and geometry of their active site loops. If the loops are not ordered properly the enzyme fails to function. Caspase-3 has four active site loops on each half of the dimer constituting the active site bundle. Proteolytic activity is dependent on cleavage of an intersubunit linker, which releases loop 2 (L2) and L2’. <scene name='Caspase-3_Regulatory_Mechanisms/Scene2_nospin_labels/1'>L2'(green spheres) interacts with the opposite half of the dimer by holding up L2 (blue spheres) </scene>. This allows L2 to make critical contacts with L3 and L4, allowing them to organize the active site, bind substrate, and orient the nucleophilic cysteine 163 (bright green) so that it can cleave after aspartate residues. | ||
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| - | Taking a closer look at L2 and L2’ we can see a critical interaction involving aspartate 169 on L2. This residue makes two hydrogen bonds with backbone amides of V189’ and E190’, stabilizing L2 in the proper position. This reinforcement allows L2 to contact L3 so as to twist the active site cysteine into the proper orientation to attack the substrate. In addition, L2 can now contact L4 at K260. This secures L4 and allows it to make contacts in the P4 position, which greatly influence substrate specificity. | ||
=Reference= | =Reference= | ||
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Hardy, J. A., J. Lam, et al. (2004). "Discovery of an allosteric site in the caspases." Proc Natl Acad Sci U S A 101(34): 12461-12466. | Hardy, J. A., J. Lam, et al. (2004). "Discovery of an allosteric site in the caspases." Proc Natl Acad Sci U S A 101(34): 12461-12466. | ||
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| + | == Importance of Loop Orientation== | ||
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| + | Caspases are extremely dependent on the orientation and geometry of their active site loops. If the loops are not ordered properly the enzyme fails to function. Caspase-3 has four active site loops on each half of the dimer constituting the active site bundle. Proteolytic activity is dependent on cleavage of an intersubunit linker, which releases loop 2 (L2) and L2’. <scene name='Caspase-3_Regulatory_Mechanisms/Scene2_nospin_labels/1'>L2'(green spheres) interacts with the opposite half of the dimer by holding up L2 (blue spheres) </scene>. This allows L2 to make critical contacts with L3 and L4, allowing them to organize the active site, bind substrate, and orient the nucleophilic cysteine 163 (bright green) so that it can cleave after aspartate residues. | ||
| + | |||
| + | Taking a closer look at L2 and L2’ we can see a critical interaction involving aspartate 169 on L2. This residue makes two hydrogen bonds with backbone amides of V189’ and E190’, stabilizing L2 in the proper position. This reinforcement allows L2 to contact L3 so as to twist the active site cysteine into the proper orientation to attack the substrate. In addition, L2 can now contact L4 at K260. This secures L4 and allows it to make contacts in the P4 position, which greatly influence substrate specificity. | ||
Revision as of 20:44, 12 December 2012
Introduction
Caspases are cysteine-dependent aspartic acid proteases and are the key facilitators of apoptosis or programmed cell death. Apoptosis is tightly regulated by these caspases, and dysregulation of caspase functions have been implicated in wide variety of diseases such as neurodegeneration, cancer, heart disease and some metabolic disorders. As such, caspases are considered to be attractive drug targets to treat these disorders.
Existing as proenzymes, caspases undergo proteolytic processing at conserved aspartate residues in their intersubunit linker to produce the large and small subunit. These subunits then dimerize to form the active enzyme. Any apoptotic signal received by the cell results in sequential activation of caspases. Upstream or initator caspases (-2,-8, -9 and -10) are first activated by forming a holoenzyme wherein they associate with another protein platform or adaptor protein. Once active, initiator caspases cleave and activate the executioner caspases (-3, -6 and -7) which in turn cleave their respective protein targets initiating cell death.
Caspase-3 structure
Caspase-3 Active Site and Loop Bundle Analysis
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Importance of Loop Orientation
Caspases are extremely dependent on the orientation and geometry of their active site loops. If the loops are not ordered properly the enzyme fails to function. Caspase-3 has four active site loops on each half of the dimer constituting the active site bundle. Proteolytic activity is dependent on cleavage of an intersubunit linker, which releases loop 2 (L2) and L2’. . This allows L2 to make critical contacts with L3 and L4, allowing them to organize the active site, bind substrate, and orient the nucleophilic cysteine 163 (bright green) so that it can cleave after aspartate residues.
Taking a closer look at L2 and L2’ we can see a critical interaction involving aspartate 169 on L2. This residue makes two hydrogen bonds with backbone amides of V189’ and E190’, stabilizing L2 in the proper position. This reinforcement allows L2 to contact L3 so as to twist the active site cysteine into the proper orientation to attack the substrate. In addition, L2 can now contact L4 at K260. This secures L4 and allows it to make contacts in the P4 position, which greatly influence substrate specificity.
Proteopedia Page Contributors and Editors (what is this?)
Scott Eron, Banyuhay P. Serrano, Alexander Berchansky, Yunlong Zhao, Jaime Prilusky, Michal Harel
