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Related Concept Videos

Caspases01:24

Caspases

Caspase, a family of cysteine proteases, serve as effectors in apoptosis. The ced3 gene in C.elegans was first identified to be involved in apoptosis. This gene encodes the ced-3 caspase that is similar to the interleukin-1-beta converting enzyme or ICE in mammals. In addition to apoptosis, caspases also function in the inflammatory response. Inflammatory caspases are essential in activating pro-inflammatory cytokines that recruit immune cells and block the replication of pathogens inside cells.
Allosteric Proteins-ATCase01:19

Allosteric Proteins-ATCase

Binding sites linkages can regulate a protein's function.  For example, enzyme activity is often regulated through a feedback mechanism where the end product of the biochemical process serves as an inhibitor.
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to  N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
The Intrinsic Apoptotic Pathway01:31

The Intrinsic Apoptotic Pathway

Internal cellular stress, such as cellular injury or hypoxia, triggers intrinsic apoptosis. The B-cell lymphoma 2 (Bcl-2) family of proteins are the primary regulators of the intrinsic apoptotic pathway. For example, during DNA damage, checkpoint proteins, such as Ataxia Telangiectasia Mutated (ATM protein) and Checkpoints Factor-2 (Chk2) proteins, are activated. These proteins phosphorylate p53 which further activates pro-apoptotic proteins, such as Bax, Bak, PUMA, and Noxa, and inhibits...
Amplifying Signals via Enzymatic Cascade01:22

Amplifying Signals via Enzymatic Cascade

When a ligand binds to a cell-surface receptor, the receptor's intracellular domain changes shape, which may either activate its enzyme function or allow its binding to other molecules. The initial signal is amplified by most signal transduction pathways. This means that a single ligand molecule can activate multiple molecules of a downstream target. Proteins that relay a signal are most commonly phosphorylated at one or more sites, activating or inactivating the protein. Kinases catalyze the...
The Extrinsic Apoptotic Pathway01:17

The Extrinsic Apoptotic Pathway

The extrinsic apoptotic pathway is initiated when extracellular death-inducing signals, such as specific cytokines, activate the death receptors expressed on the cell surface. The immune cells involved in this pathway are natural killer cells (NK cells) and cytotoxic T-lymphocytes. NK cells are critical in innate immune response, while cytotoxic T-lymphocytes are associated with adaptive immune response. These cells recognize specific receptors expressed on the altered cells and activate...
Intracellular Signaling Cascades01:24

Intracellular Signaling Cascades

Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. The continuation of a signal in this manner is called signal transduction. Signal transduction only occurs with cell-surface receptors, which cannot interact with most components of the cell, such as DNA. Only internal receptors can interact directly with DNA in the nucleus to initiate protein synthesis. When a ligand binds to its receptor, conformational changes occur that affect the...

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Lighting Up the Pathways to Caspase Activation Using Bimolecular Fluorescence Complementation
08:47

Lighting Up the Pathways to Caspase Activation Using Bimolecular Fluorescence Complementation

Published on: March 5, 2018

An allosteric circuit in caspase-1.

Debajyoti Datta1, Justin M Scheer, Michael J Romanowski

  • 1Departments of Pharmaceutical Chemistry and Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, CA 94143, USA.

Journal of Molecular Biology
|July 2, 2008
PubMed
Summary
This summary is machine-generated.

Structural studies of caspase-1 reveal a critical allosteric circuit. A small subset of side chains, particularly a salt bridge, dictates enzyme activity and site-to-site coupling.

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Lighting Up the Pathways to Caspase Activation Using Bimolecular Fluorescence Complementation
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Published on: March 24, 2023

Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Caspase-1 is a dimeric thiol protease.
  • It exists in active and inactive states regulated by active site occupancy or allosteric ligands.
  • A hydrogen bond network connects active and allosteric sites.

Purpose of the Study:

  • To identify critical residues in the allosteric network of caspase-1.
  • To elucidate the mechanism of allosteric regulation and site-to-site coupling.

Main Methods:

  • Alanine-scanning mutagenesis of nine key side chains.
  • X-ray crystallography of caspase-1 variants.
  • Enzyme kinetics measurements (k(cat)/K(m)).

Main Results:

  • Only two side chains, Arg286 and Glu390 forming a salt bridge, significantly reduced catalytic efficiency (100-200 fold) upon mutation.
  • Minor effects were observed for neighboring residues Ser332 and Ser339 (4-7 fold reduction).
  • Mutations in the salt bridge, including R286K, drastically reduced activity, highlighting its importance.

Conclusions:

  • A small subset of residues, forming a contiguous 'hot wire' circuit, is critical for caspase-1 activity and allosteric regulation.
  • The salt bridge and solvent coordination near the allosteric site are crucial for enzyme function.
  • This circuit facilitates site-to-site communication within the dimeric enzyme.