The protein of the month award goes to any protein that can monopolise my interest for at least an hour. This month, the award goes to Nepenthesin, an aspartic protease found in the pitchers of Nepenthes plants.
Also known as Monkey Cups, Nepenthes are a species of carnivorous plants that inhabit tropical regions such as Borneo, Malaysia, Indonesia, Sumatra, and the Philippines. The prey usually consists of insects, but some of the larger species can consume small mammals, lizards and frogs.
The trap itself contains a fluid that traps, kills and breaks down the prey. There are many interesting molecules in this fluid, including some viscoelastic biopolymers that allow the fluid to retain a high viscosity even when quite dilute. However, this month’s protein is Nepenthesin.
A protease is an enzyme that can break down proteins by cleaving the amino acids that all proteins are comprised of. The different amino acids form a ‘backbone’ to the protein, and the amino acids are joined together by peptide bonds. These peptide bonds are the site of protease cleavage, the cleavage occurring near to specific amino acids.
Proteases are also named for the chemical reaction involved in cleavage. For example, Nepenthesin is an aspartic protease, so the cleavage of the peptide bonds is done via an aspartic acid residue within the protease. Nepenthesin cleaves peptide bonds in the target protein on either side of an aspartic acid residue or between a lysine residue and an asparagine residue.
Nepenthesin is used by the Nepenthes plants to break down the protein components of its prey so that the amino acids can be absorbed by the plant and used to assemble into proteins of its own. Its remarkably similar to how proteins are broken down in the mammalian stomach aswell.
In fact, Nepenthesin does bear a striking similarity to pepsin, an aspartic protease found in the stomachs of mammals, birds, reptiles and fishes.