CHYMOTRYPSIN

3D Structure of CHYMOTRYPSIN

CPK Color Scheme C O N P S

Chymotrypsin is a digestive enzyme that is secreted by the pancreas. It belongs to the family of enzymes called serine proteases that includes trypsin. These proteins cleave proteins into smaller peptides, and the side chain of serine plays a catalytice role in this cleavage. Chymotrypsin hydrolyzes the peptide bond of amino acids with large hydrophobic side chains, such as phenylalanine, tryptophan, and tyrosine.

Explore the structural aspects of chymotrypsin's enzymatic action below!

IMAGE 1

Chymotrypsin consists of 3 chains, A (Blue), B (Aqua), and C (Green). It is derived from the precursor chymotrypsinogen, which is 245 amino acid residues long. The three separate chains of the activated chymotrypsin are formed when two dipeptide units, consisting of residues 14 and 15 and residues 147 and 148 are removed. Click

here.

Here you see highlighted the three amino acids that define the active site. Serine 195 (yellow), Histidine 57(blue), Aspartic Acid 102 (red). These three residues are directly involved the enzymatic reaction. The reaction is accomplished by an acylation of serine, followed by the regeneration of the active site and the resultant peptide cleavage. Click

here.

To reset Image 1, Click

here

IMAGE 2

The interactions of the three peptide chains of chymotrypsin are not disrupted when chymotrypsinogen is cleaved at the above mentioned sites because of the intermolecular forces already present. To see the disulfide bridges present in this protein Click

here.
There are a total of five disulfide bridges. These are shown as green lines between the two orange cysteine residues.

To reset Image 2 Click

here.

IMAGE 3

In this last image, the binding site can be seen highlighted in yellow.This hydrophobic pocket is where the target peptide is positioned for cleavage. Click

here.

To see where the Ser, His and Asp are in this pocket Click here

for Ser,
here

for His,
and here

for Asp.

To see an example of substrate in the active site, Scroll back to Image 1 and Click

here. This is an engineered pentapeptide sitting in the binding site.

REFERENCES:
Ege, S. N. Organic Chemistry: Structure and Reactivity, 4th ed. New York: Houghton Mifflin Co., 1999.

Niemann, Carl. 1964 Mar 20. Alpha-Chymotrypsin and the Nature of Enzyme Catalysis. Science. 143(3612): 1287-1296.