N-terminal domain of the beta-propeller phytase of Pseudomonas sp. FB15 plays a role for retention of low-temperature activity and catalytic efficiency

Pseudomonas sp. FB15 producing phytase with a high activity at low temperature was isolated from foreshore soil. The phytase gene was cloned and sequenced. Molecular modeling predictions using its amino acid sequence indicated that it belongs to the group of beta-propeller phytases (BPPs). However, it differs from the conventional structure of BPPs in the number of propeller-shaped domains. Most BPPs have a propeller with six blades that consist of four or five beta-sheets. However, the BPP from the isolated strain contained a C-terminal domain containing a conserved BPP sequence and also an N-terminal domain consisting of an additional 275 amino acids. The characterization of recombinant BPP from Pseudomonas sp. FB15 (PSphy) revealed the highest activity to be at pH 6 and 40 °C. Additionally, it showed that more than 80% of optimal activity was retained at a relatively low temperature of 25 °C. In addition, CaCl2 was required for activity, and the optimal concentration of CaCl2 was 4 mM. The activity at low temperature was reduced in a recombinant protein from which the N-terminal domain was removed, as was catalytic efficiency. These results suggest that the N-terminal domain is required for the low temperature activity and high catalytic efficiency of PSphy.