Purification and structural analysis of an abundant thaumatin-like proteinfrom ripe banana fruit

The pulp of ripe bananas (Musa acuminata) contains an abundant thaumatin-li ke protein (TLP). Characterization of the protein and molecular cloning of the corresponding gene from banana demonstrated that the native protein con sists of a single polypeptide chain of 200 amino acid residues. Molecular m odelling further revealed that the banana thaumatin-like protein (Ban-TLPP adopts an overall fold similar to that of thaumatin and thaumatin-like PR-5 proteins. Although the banana protein exhibits an electrostatically polari zed surface, which is believed to be essential for the antifungal propertie s of TLPs, it is apparently devoid of antifungal activity towards pathogeni c fungi. It exhibits a low but detectable in vitro endo-beta -1,3-glucanase (EC 3.2.1.x) activity. As well as being present in fruits, Ban-TLP also oc curs in root tips where its accumulation is enhanced by methyl jasmonate tr eatment of plants. Pulp of plantains (Musa acuminata) also contains a very similar TLP, which is even more abundant than its banana homologue. Our res ults demonstrate for the first time that fruit-specific (abundant) TLPs are not confined to dicots but occur also in fruits of monocot species. The po ssible role of the apparent widespread accumulation of fruit-specific TLPs is discussed.