cysteine-type endopeptidase activity

Definition

Target type: molecularfunction

Catalysis of the hydrolysis of internal, alpha-peptide bonds in a polypeptide chain by a mechanism in which the sulfhydryl group of a cysteine residue at the active center acts as a nucleophile. [GOC:mah, https://www.ebi.ac.uk/merops/about/glossary.shtml#CATTYPE, https://www.ebi.ac.uk/merops/about/glossary.shtml#ENDOPEPTIDASE]

Cysteine-type endopeptidase activity refers to the catalytic hydrolysis of peptide bonds within a polypeptide chain. This activity is characterized by the presence of a cysteine residue within the active site of the enzyme, which acts as a nucleophile in the reaction mechanism. The catalytic process typically involves the following steps:

1. **Substrate Binding:** The enzyme binds to the substrate protein, positioning the peptide bond to be cleaved near the active site.

2. **Nucleophilic Attack:** The cysteine residue in the active site attacks the carbonyl carbon of the peptide bond, forming a covalent intermediate.

3. **Intermediate Formation:** The covalent intermediate is unstable and rapidly breaks down, releasing the N-terminal fragment of the substrate and forming a thioester bond between the enzyme and the C-terminal fragment.

4. **Water Attack:** A water molecule then attacks the thioester bond, releasing the C-terminal fragment and regenerating the active enzyme.

Cysteine-type endopeptidases are highly diverse and play critical roles in a wide range of cellular processes, including:

* **Protein Degradation:** Cysteine proteases are essential for the breakdown of proteins, both within the cell and in extracellular spaces.
* **Signal Transduction:** Some cysteine proteases act as signaling molecules, regulating various cellular processes by cleaving specific target proteins.
* **Immune Response:** Cysteine proteases are involved in the immune response by degrading pathogens and activating immune cells.
* **Development and Differentiation:** Cysteine proteases play important roles in cell development and differentiation by regulating the expression and activity of key proteins.

Examples of cysteine-type endopeptidases include:

* **Cathepsins:** A family of lysosomal proteases involved in protein degradation and other cellular processes.
* **Caspases:** A family of proteases that execute programmed cell death (apoptosis).
* **Calpains:** A family of calcium-dependent proteases involved in various cellular functions, including cell signaling and cytoskeletal remodeling.
* **Papain:** A plant cysteine protease used as a meat tenderizer and in the pharmaceutical industry.

The specific function of a particular cysteine-type endopeptidase is determined by its substrate specificity, which is dictated by the amino acid sequence surrounding the active site and the three-dimensional structure of the enzyme.'
"

Proteins (49)

Compounds (634)