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Chymotrypsin, trypsin, and elastase all share the same catalytic mechanism, but have different specificities. (a) These proteases are considered serine proteases because the active sites contain serine, histidine and aspartate. Describe the roles that each of these amino acid residues play in hydrolyzing protein substrates. (b) The active site pockets of chymotrypsin, trypsin, and elastase are shown in the image below. Based on the image, which side chain of the amino acids would they prefer to cleave respectively, Ala, Arg, or Trp? Explain your answers. Val 190 Val 216 Asp 189 Chymotrypsin Trypsin Elastase

Chymotrypsin, trypsin, and elastase all share the same catalytic mechanism, but have different specificities. (a) These proteases are considered serine proteases because the active sites contain serine, histidine and aspartate. Describe the roles that each of these amino acid residues play in hydrolyzing protein substrates. (b) The active site pockets of chymotrypsin, trypsin, and elastase are shown in the image below. Based on the image, which side chain of the amino acids would they prefer to cleave respectively, Ala, Arg, or Trp? Explain your answers. Val 190 Val 216 Asp 189 Chymotrypsin Trypsin Elastase

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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**Title: Understanding the Specificities of Serine Proteases: Chymotrypsin, Trypsin, and Elastase** Chymotrypsin, trypsin, and elastase all share the same catalytic mechanism but exhibit different substrate specificities. (a) **Serine Proteases Overview:** These proteases are categorized as serine proteases because their active sites contain the amino acids serine, histidine, and aspartate. These residues play crucial roles in hydrolyzing protein substrates. - **Serine** acts as a nucleophile that attacks the peptide bond. - **Histidine** assists in the proton transfer process. - **Aspartate** helps orient the histidine and stabilizes the charge. (b) **Active Site Specificities:** The active site pockets of these proteases show distinct preferences for amino acid residues. The image below illustrates the structural differences: - **Chymotrypsin**: Prefers to cleave aromatic amino acids due to its large pocket. - **Trypsin**: Contains an aspartate residue (Asp 189) at the bottom of its active site pocket, enabling it to bind and cleave positively charged side chains like arginine (Arg) and lysine. - **Elastase**: Has valine residues (Val 216 and Val 190) creating a narrow pocket, thus preferring smaller, neutral amino acids like alanine (Ala). **Diagram Explanation:** - **Chymotrypsin**: Illustrated by a broad, deep pocket. - **Trypsin**: Features a narrower pocket with a negatively charged Asp residue at the bottom. - **Elastase**: Shows a shallow and large pocket bound by Val residues, restricting access to larger side chains. Understanding these interactions aids in comprehending how these enzymes achieve their substrate specificity through structural differences in their active site pockets.
Transcribed Image Text:**Title: Understanding the Specificities of Serine Proteases: Chymotrypsin, Trypsin, and Elastase** Chymotrypsin, trypsin, and elastase all share the same catalytic mechanism but exhibit different substrate specificities. (a) **Serine Proteases Overview:** These proteases are categorized as serine proteases because their active sites contain the amino acids serine, histidine, and aspartate. These residues play crucial roles in hydrolyzing protein substrates. - **Serine** acts as a nucleophile that attacks the peptide bond. - **Histidine** assists in the proton transfer process. - **Aspartate** helps orient the histidine and stabilizes the charge. (b) **Active Site Specificities:** The active site pockets of these proteases show distinct preferences for amino acid residues. The image below illustrates the structural differences: - **Chymotrypsin**: Prefers to cleave aromatic amino acids due to its large pocket. - **Trypsin**: Contains an aspartate residue (Asp 189) at the bottom of its active site pocket, enabling it to bind and cleave positively charged side chains like arginine (Arg) and lysine. - **Elastase**: Has valine residues (Val 216 and Val 190) creating a narrow pocket, thus preferring smaller, neutral amino acids like alanine (Ala). **Diagram Explanation:** - **Chymotrypsin**: Illustrated by a broad, deep pocket. - **Trypsin**: Features a narrower pocket with a negatively charged Asp residue at the bottom. - **Elastase**: Shows a shallow and large pocket bound by Val residues, restricting access to larger side chains. Understanding these interactions aids in comprehending how these enzymes achieve their substrate specificity through structural differences in their active site pockets.
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