Thaumatin [ PUBMED:7049841 ] is an intensely sweet-tasting protein, 100 000 times sweeter than sucrose on a molar basis [ PUBMED:7049841 ], found in berries from Thaumatococcus daniellii, a tropical flowering plant known as Katemfe. It is induced … expand

Thaumatin [ PUBMED:7049841 ] is an intensely sweet-tasting protein, 100 000 times sweeter than sucrose on a molar basis [ PUBMED:7049841 ], found in berries from Thaumatococcus daniellii, a tropical flowering plant known as Katemfe. It is induced by attack by viroids, which are single-stranded unencapsulated RNA molecules that do not code for protein.

Thaumatin consists of about 200 residues and contains 8 disulphide bonds. Like other PR proteins, thaumatin is predicted to have a mainly β structure, with a high content of β-turns and little helix [ PUBMED:7049841 ]. Several stress-induced proteins of plants have been found to be related to thaumatins:

• A maize alpha-amylase/trypsin inhibitor
• Two tobacco pathogenesis-related proteins: PR-R major and minor forms, which are induced after infection with viruses
• Salt-induced protein NP24 from tomato
• Osmotin, a salt-induced protein from tobacco [ PUBMED:16666857 ]
• Osmotin-like proteins OSML13, OSML15 and OSML81 from potato [ PUBMED:7630973 ]
• P21, a leaf protein from soybean
• PWIR2, a leaf protein from wheat [ PUBMED:1650615 ]
• Zeamatin, a maize antifungal protein [ PUBMED:7846159 ]

This family is also referred to as pathogenesis-related group 5 (PR5), as many thaumatin-like proteins accumulate in plants in response to infection by a pathogen and possess antifungal activity [ PUBMED:1463856 ]. The proteins are involved in systemically acquired resistance and stress response in plants, although their precise role is unknown [ PUBMED:1463856 ]. The PR5K receptor protein kinase from Arabidopsis comprises an extracellular domain related to the PR5 proteins, and an intracellular protein-serine/threonine kinase domain [ PUBMED:8637920 ].