Protein stability in the amorphous carbohydrate matrix: relevance to anhydrobiosis

The formation of intracellular glass is proposed to be relevant to protein stabilization and survival of anhydrobiotic organisms in the dry state. The stability of proteins in the amorphous carbohydrate matrix and its relevance to seed survival have been investigated in the present study. Glucose-6-phosphate dehydrogenase (G6PDH) was preserved in the amorphous glucose/sucrose (1:10, w/w) matrix by freeze-drying. The stability of freeze-dried G6PDH was examined at temperatures above and below the glass transition temperature (Tg). The rate of G6PDH inactivation in the amorphous carbohydrate matrix deviated significantly from the Arrhenius kinetics, and conformed to the Williams-Landel-Ferry (WLF) relationship. The temperature dependence of G6PDH inactivation in two sets of samples with different Tg values was compared. Identical temperature dependence of G6PDH inactivation was observed after temperature normalization by (T-Tg). Seed survival of Vigna radiata Wilczek (mung bean) showed a similar WLF kinetics at storage temperatures T > or = Tg. In situ protein stability in mung bean embryonic axes was studied using differential scanning calorimetry (DSC). Thermal stability of seed proteins exhibited a strong dependence on the Tg of intracellular glass. These results indicate an important role of the glassy state in protein stabilization. Our data suggest an association between protein stability in intracellular glass and seed survival during storage.