Pepsin digests proteins in strong stomach acid
A Tricky Business
A Piece of Scientific History
The acid proteases have evolved to fill several functional roles in different organisms. Pepsin, shown at upper left (PDB entry 5pep ), is optimized for digestion of food in the acidic environment of the stomach. It is very promiscuous, cleaving proteins in many different places. Chymosin, shown at upper right (PDB entry 4cms ), is made by young calves to break down milk proteins. A purified form of chymosin, taken from calf stomach, has been used for centuries to curdle milk in the production of cheese. Cathepsin D, shown at lower left (PDB entry 1lyb ), digests proteins inside lysozomes, the tiny stomachs inside cells. Other cellular acid proteases, such as renin (not shown, PDB entry 1hrn ), are designed to make very specific cuts in one particular protein, aiding in the maturation of a hormone or structural protein. Endothiapepsin, shown at lower right (PDB entry 4ape ), is made by a fungus and excreted into the surrounding environment, breaking up the surrounding proteins and allowing the fungus to feed on the pieces.
Exploring the Structure
These illustrations were created with RasMol. You can create similar illustrations by clicking on the PDB accession code and picking one of the options for 3D viewing. To highlight the active site aspartates, select residues numbered 32 and 215 in this structure file.
December 2000, David Goodselldoi:10.2210/rcsb_pdb/mom_2000_12