Thermostability engineering of fungal phytases using low-M-r additives andchemical crosslinking

With the ultimate goal to develop preparations of phytase (myo-inositol hex akisphosphate phosphohydrolase) with improved thermal resistance for inclus ion in animal feed, several thermostabilization approaches were investigate d with a set of fungal (Aspergillus fumigatus, Aspergillus nidulans, Asperg illus terreus, and Aspergillus niger phytase) and consensus phytases. Scree ning of different low-M, additives revealed that polyethylene glycols incre ase the thermostability of all phytases in a molecular weight-dependent fas hion. The polyols ribitol, xylitol (C-5 sugars) and sorbitol (C-6 sugar) al so improved their thermostability, whereas polyols containing more or less carbon atoms, such as glycerol, erythritol and mannoheptulose, showed only minor effects. The stabilizing effects of PEGs and polyols were concentrati on dependent. In a second series of experiments, crosslinking of the carboh ydrate chains of A. fumigatus and consensus phytase using sodium periodate and adipic acid dihydrazide resulted in the formation of oligomeric forms, which may explain the observed thermostability enhancement of 10-15 degrees C.