title: Crystal structure of the intensely sweet protein monellin.
abstract: Two unusual proteins, discovered in African berries, possess the interesting property of having a very high specificity for the sweet receptors. These proteins, monellin and thaumatin, are approximately 100,000 times sweeter than sugar on a molar basis and several thousand times sweeter on a weight basis. Neither contains carbohydrates or modified amino acids. Several interesting observations have been made about the two proteins: native conformations are important for the sweet taste, although both proteins are intensely sweet, there are no statistically significant sequence similarities between them; and despite the absence of sequence similarity, antibodies against thaumatin compete for monellin (as well as many other sweet compounds, but not for chemically modified non-sweet monellin) and vice versa. To understand the structural basis of these observations we determined the crystal structure of thaumatin, and report here the structure of monellin at 3 A resolution. Monellin consists of two peptide chains, the A chain of 44 residues and the B chain of 50 residues. We find no similarity between the backbone structure of monellin and that of thaumatin.
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D010936:Plant Extracts; D010940:Plant Proteins; D011487:Protein Conformation; D013549:Sweetening Agents; D013649:Taste
chemical_list: D010936:Plant Extracts; D010940:Plant Proteins; D013549:Sweetening Agents; C002541:monellin protein, Dioscoreophyllum cumminsii; C003427:thaumatin protein, plant