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TrypsinTrypsin
Trypsin is a medium sized, globular, digestive serine protease that is synthesized by the pancreas and secreted into the duodenum of the small intestine. Trypsin hydrolyzes peptide bonds based on side chain specificities of the amino acids surrounding the bond to be cleaved. Trypsin's specificity is for the positively charged side chains of lysine and arginine.
StructureStructure
Trypsin's primary structure is a polypeptide chain of 237 amino acids. These amino acids interact with each other mostly through hydrogen bonding to form trypsin's secondary structural units. Trypsin has many important , including two alpha helices (blue), an anti-parallel beta sheet (green), and random coils (gray). The arrows on these elements point toward the carboxy terminus of the protein. These secondary structures interact together to form the fully folded, native trypsin.
Polar and Nonpolar ResiduesPolar and Nonpolar Residues
Trypsin's distribution of follow the rules of the hydrophobic effect. The nonpolar (gray) residues are located on the interior of the protein so they can be shielded from water, while the polar (purple) residues are distributed on the exterior of the protein because they can interact with water. This model shows the distribution of the hydrophilic and hydrophobic residues and the actual space they occupy. Again the hydrophobic, nonpolar residues are shown in gray, and the hydrophilic, polar residues are purple. This type of residue distribution in trypsin is entropically favorable becuase the water surrounding the protein does not become ordered. In this figure the can be seen. The puprle polar residues are the residues that are interacting with the red water molecules.
Attractions Between Structural Components and the Remainder of the ProteinAttractions Between Structural Components and the Remainder of the Protein
Disulfide BondsDisulfide Bonds
Trypsin contains three involving six cysteine residues. These disulfide bonds are intramolecular forces that stabalize the tertiary structure of Trypsin. The figure shows the yellow disulfide bonds between the cysteine residues connecting two random coils, connecting one of the alpha helices to the beta sheet, and the other disulfide connecting the two alpha helices.
Residue ChargeResidue Charge
This shows the different charges of the amino acid residues that make up Trypsin. The blue residues have cationic side chains, the red residues have anionic side chains, the light purple are the polar, uncharged residues, and the gray residues are hydrophobic. When compared to the spacefilled figure above, the direct correlation between polarity of the side chain and charge of the side chain can be seen. Those residues with charged (blue and red) side chains as well as the polar, uncharged residues are the residues on the exterior of the protein, while the hydrophobic residues remain at the protein's core. Those residues that are cationic and anionic are able to participate in salt bridges.
Ion ContactsIon Contacts
Trypsin interacts with four . The red and yellow atoms are the ions. The yellow atoms are sulfur and the red atoms are oxygen.
Catalytic MechanismCatalytic Mechanism
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