Brazzein

Protein

Brazzein is a protein found in the West African fruit of Oubli (Pentadiplandra brazzeana Baillon). It was first isolated by the University of Wisconsin–Madison in 1994. Brazzein is found in the extracellular region, in the pulp tissue surrounding the seeds. With pentadin, discovered in 1989, brazzein is the second sweet tasting protein discovered in the Oubli fruit. Like the other sweet proteins discovered in plants, such as monellin and thaumatin, it is extremely sweet compared to commonly used sweeteners (500 to 2000 times sweeter than sucrose). The fruit tastes sweet to humans, monkeys, and bonobos, but gorillas have mutations in their sweetness receptors so that they do not find brazzein sweet, and they are not known to eat the fruit.

The Oubli plant (from which the protein was isolated) grows in Gabon and Cameroon, where its fruit has been consumed by the apes and local people for a long time. Due to brazzein and pentadin, the berries of the plant are incredibly sweet. Locals call them "Oubli" (French for "forgot") in their vernacular language because their taste is said to encourage nursing infants to forget their mother's milk, as once they eat them they are said to forget to come back to the village to see their mother.

The monomer protein, consisting of 54 amino acid residues, is the smallest of the sweet proteins with a molecular weight of 6.5 kDa.'' The structure of brazzein was determined by proton nuclear magnetic resonance (NMR) at a pH of 5.2 and 22 °C. Brazzein has four evenly spaced disulfide bonds and no sulfhydryl groups. 3D analysis of brazzein showed one alpha helix and three strands of anti parallel beta sheet. This is not superficially similar to either of the other two sweet tasting proteins, monellin and thaumatin. However, a recent 3D study shows that these three proteins possess similar "sweet fingers" believed to elicit the sweet taste. Residues 29–33 and 39–43, plus residue 36, as well as the C terminus were found to be involved in the sweet taste of the protein. The charge of the protein also plays an important role in its interaction with the sweet taste receptor.