Antimicrobial Activity of Malting Barley Grain Thaumatin-Like Protein Isoforms, S and R

Abstract

Two basic proteins were isolated to homogeneity from malting barley (Hordeum vulgare L.) grain. Proteins were identified as members of a Thaumatin-Like Protein (TLP) family, by Western blot. Isoforms, assigned as TLP-S and TLP-R, have slightly different mobility at about 22 and 27 kDa in nonreducing and reducing conditions, and pI values of 9.5 and 9.4, respectively. The antifungal potency of malting barley grain TLPs isoforms was examined on Micrococcus lysodeikticus, Saccharomyces cerevisiae, Candida albicans and plant pathogen Fusarium sporotrichioides growth in vitro. It was found that that IC50 value for TLP-S was two fold higher. Antibacterial and antifungal activities of both isoforms were completely abolished by divalent (Ca2+, Mn2+, Mg2+) and monovalent (K+) cations, at concentrations approximating physiological ionic strength and higher. Glucanase activity was not observed; neither TLP-S nor TLP-R digested glucan. On the basis of these results, the importance of TLP for barley grain protection against fungal diseases has been discussed together with the mechanism of antimicrobial action.