Compare and contrast serine proteases and aspartic proteases. Not all answers will be used. Serine protease Both Aspartic protease Answer Bank two aspartic acids in active site tetrahedral intermediate trigonal planar intermediate direct electrophilic attack by water catalytic triad of serine, leucine, and valine covalent intermediate direct nucleophilic attack by water four aspartic acids in active site catalytic triad of serine, histidine, and aspartic acid
The Correct Answer and Explanation is :
Serine Proteases vs. Aspartic Proteases:
- Serine Protease:
- Catalytic triad of serine, histidine, and aspartic acid
- Tetrahedral intermediate
- Covalent intermediate
- Direct nucleophilic attack by water
- Direct electrophilic attack by water (not typically associated with serine proteases)
- Aspartic Protease:
- Two aspartic acids in the active site
- Trigonal planar intermediate
- No covalent intermediate
- Direct electrophilic attack by water
- Catalytic triad of serine, leucine, and valine (incorrect)
Explanation:
Serine proteases and aspartic proteases are both essential classes of enzymes that catalyze the hydrolysis of peptide bonds, but they differ significantly in their mechanisms and structures.
- Catalytic Mechanism:
- Serine Proteases: These enzymes have a catalytic triad consisting of serine, histidine, and aspartic acid. The serine residue is the key nucleophile, attacking the peptide bond, forming a tetrahedral intermediate. This results in the formation of a covalent intermediate between the enzyme and the substrate. Water is then used to break the bond, regenerating the enzyme and completing the hydrolysis.
- Aspartic Proteases: These enzymes typically use two aspartic acids in the active site. The reaction involves a trigonal planar intermediate, and the active site is not involved in forming a covalent bond with the substrate. Instead, the two aspartates facilitate direct electrophilic attack by water, enabling the hydrolysis of the peptide bond.
- Structural Differences:
- Serine Proteases: The key structural feature is the presence of a catalytic triad of serine, histidine, and aspartic acid, which work together to activate the nucleophilic serine.
- Aspartic Proteases: These enzymes feature a pair of aspartic acid residues in the active site that play a role in proton transfer, making it more efficient for electrophilic attack on the peptide bond.
In conclusion, while both types of proteases perform similar tasks in peptide bond cleavage, their catalytic strategies and active site compositions differ. Serine proteases utilize a triad of amino acids and form covalent intermediates, whereas aspartic proteases rely on a pair of aspartic acids and direct electrophilic water attack.