|PDB||1BRZ (RCSB PDB PDBe PDBj) More structures|
Brazzein is a sweet-tasting protein extracted from the West African fruit of the climbing plant Oubli (Pentadiplandra brazzeana Baillon). It was first isolated as an enzyme by University of Wisconsin–Madison in 1994.
Brazzein is found in the extracellular region. It is found in the pulp tissue surrounding the seeds.
The plant grows in Gabon and Cameroon, where the fruit has been consumed by the apes and local people for a long time. The berries of the plant are incredibly sweet. African locals call them "Oubli" (French for "forgot") in their vernacular language because their taste helps nursing infants 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 weigh of 6.5 kDa. The amino acid sequence of brazzein, adapted from the Swiss-Prot biological database of protein, is as follows: QDKCKKVYEN YPVSKCQLAN QCNYDCKLDK HARSGECFYD EKRNLQCICD YCEY
The structure of brazzein was determined by proton nuclear magnetic resonance (NMR) at a pH 5.2 and 22 degrees C.. Brazzein has four evenly spaced disulfide bonds and no sulfhydryl groups.
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 tasting of the protein. The charge of the protein plays also an important role in its interaction with the sweet taste receptor.
Based on this knowledge a synthesised improved brazzein, called pGlu-1-brazzein, was reported to be twice sweet as the natural counterpart.
On weight basis, brazzein is 500 to 2000 times sweeter than sugar, compared to 10% sugar and 2% sugar solution respectively.
Its sweet perception is more similar to sucrose than that of thaumatin with a clean sweet taste with lingering aftertaste and with a slight delay longer than aspartame in an equi-sweet solution.
As a sweetener
Unlike other natural sweeteners, apart from thaumatin, its sweet profile is closer to sucrose. Unlike other sweet-tasting proteins, it can withstand heat which makes it suitable for industrial food manufacture.
Increasing interest of brazzein makes it difficult to source naturally from Gabon, but it can also be synthesised by a solid-phase method. Recombinant proteins were successfully produced via E. coli.
The Texas companies Prodigene and Nectar Worldwide were among the licensees to use Wisconsin Alumni Research Foundation patents on brazzein, and genetically engineer the enzyme into maize. Brazzein then can be commercially extracted from maize through ordinary milling. Approximately one ton of maize yields 1-2 kilograms of Brazzein. It can also be engineered into plants like wheat to make pre-sweetened grains, e.g. for cereals.
Despite the fact that the sweet taste of the berries was well known in West Africa, the University claims that the sweet compound (brazzein) is its own invention and admit to no connection with the Gabon.
This fact, which involved appropriation of legal rights by means of patents over indigenous biomedical knowledge without compensation to the indigenous groups, is considered an act of Biopiracy by GRAIN and Green Peace.
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- UniProtKB/Swiss-Prot database entry #PP56552
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- US patent 5326580, Hellekant BG, Ming D, "Brazzein sweetener", issued 1994-07-05
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