Lipase, as its name suggests, is an enzyme responsible for the cleavage of types of lipid molecules. There are different types of lipases, many of which work in similar ways. For instance, Human Pancreatic Lipase, or HPL, splits triglycerides, the main lipids in the human diet, into glycerol and three fatty acids. The structure shown at right is that of Horse Pancreatic Lipase. It consists of two identical subunits, totaling 449 amino acids each.

The of lipase (just one subunit) include 102 residues which create 13 alpha helices, shown in red, and 139 residues involved in beta sheets totaling 28 strands, shown in gold. Lipase of course consists of both . The polar residues in this scene are shown in a light blue shade, and the nonpolar are in a dark red. From this representation, it can be assumed that there is a similar quantity of polar residues as there are nonopolar. The tertiary stucture of the molecule is stabilized by 6 and ionic interactions with a calcium ligand. Finally, the quaternary structure is completed by the adjoining of the two identical subunits.

The Calcium Ligand

The are two calcium ions, one buried within each subunit. This scene shows the interactions between the calcium ion in subunit A and the following residues from subunit A: GLU187, ARG190, ASP192, and ASP195. In addition to interactions with these molecules, the calcium ion is also stabilized by the oxygens from two water molecules shown in pink. These interactions between the amino acid residues and the ligand are crucial for proper protein folding, and subsequently protein function.

The Mechanism