Catalytic Mechanism of Chymotrypsin slide 1 • Chymotrypsin – Protease: catalyze hydrolysis of proteins in small intestine – Specificity: Peptide bond on carboxyl side of aromatic side chains (Y, W, F) & Large hydrophobic residues (Met,…) – Three polypeptide chains cross-linked to each other – Three catalytic residues: Ser195, His57, & Asp102
14
Embed
Catalytic Mechanism of Chymotrypsin slide 1 Chymotrypsin –Protease: catalyze hydrolysis of proteins in small intestine –Specificity: Peptide bond on carboxyl.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Catalytic Mechanism of Chymotrypsin slide 1
• Chymotrypsin
– Protease: catalyze hydrolysis of proteins in small intestine
– Specificity: Peptide bond on carboxyl side of aromatic side chains (Y, W, F) & Large hydrophobic residues (Met,…)
– Three polypeptide chains cross-linked to each other
– Three catalytic residues: Ser195, His57, & Asp102
Catalytic Mechanism of Chymotrypsin slide 2
Catalytic Mechanism of Chymotrypsin slide 2
Catalytic Mechanism of Chymotrypsin slide 3
Catalytic Mechanism of Chymotrypsin slide 4
Summary for the Catalytic Mechanism of Chymotrypsin
• Mechanism
– General acid-base catalysis & Covalent catalysis
– Two steps: Acylation &
Deacylation (rate limiting; reverse of acylation with water substituting the amine component)
– Key features
• Active Ser195 & roles of the three catalytic residues
• Tetrahedral transition state
• Oxyanion and Oxyanion hole
• Acyl-enzyme intermediate
Serine Protease FamilyChymotrypsin & elastase main chain conformation
Substrate Binding Induces Large Structural Changes at the Active Site
Substrate Binding at the Active Site
Catalytic Mechanism of Carboxypeptidase A• The H2O molecule is activated by
– Bound Zn2+ and COO– of Glu270• Activated H2O attacks the C=O group of the scissile peptide
bond• Glu270 simultaneously accepts a H+ from H2O• A negatively charged tetrahedral intermediate is formed• Intermediate is stabilized by Zn2+ and Arg127• H+ transfer from COOH of Glu270 to the peptide NH• Peptide bond is concomitantly cleaved• The reaction products diffuse away• Summary:
– Activation of H2O by Zn2+ and Glu270– Proton abstraction and donation by Glu270– Electrostatic stabilization of tetrahedral intermediate by