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Phytase activity in Aspergillus fumigatus isolates
E J Mullaney1, C B Daly, K Sethumadhavan
1Southern Regional Research Center, U.S. Department of Agriculture, New Orleans, Louisiana 70124, USA.
Abstract:
Extracellular phytase from Aspergillus fumigatus isolates was characterized and their genes were cloned and sequenced. Based on their banding pattern in SDS-PAGE all phytases were found to be glycosylated and have similar molecular mass. A correlation between lower optimum pH (4.0) and a higher optimum temperature (70 degrees C) was found in these enzymes. All enzymes characterized displayed a lower specific activity for phytic acid and were more susceptible to proteolytic degradation than the Aspergillus niger phytase that is now commercially available. DNA sequencing established almost no sequence variation in any of the genes and no correlation is evident between a specific amino acid sequence and any physicochemical and catalytic properties of the enzymes. Despite two of the isolates having identical deduced amino acid sequence, characterization of the enzymes encoded by these two identical genes revealed differences in both pH and temperature optimum. This suggests that differences in pH and temperature optimum in these four isolates of A. fumigatus may be due in part to subtle differences in posttranslational modification.
Insights
Extracellular phytase from Aspergillus fumigatus shows glycosylation and similar molecular mass. Differences in enzyme properties suggest post-translational modifications influence function, despite identical gene sequences.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Extracellular phytases are crucial enzymes for phosphorus liberation.
- Aspergillus fumigatus is a source of phytase, but its properties require detailed characterization.
- Understanding phytase variations is key for industrial applications.
Purpose of the Study:
- To characterize extracellular phytases from Aspergillus fumigatus isolates.
- To clone and sequence the genes encoding these phytases.
- To investigate the relationship between gene sequence, protein properties, and enzyme function.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for glycosylation and molecular mass analysis.
- Enzyme activity assays to determine specific activity, optimal pH, and optimal temperature.
- DNA sequencing to analyze gene variations.
- Proteolytic degradation assays.
Main Results:
- All characterized phytases were glycosylated with similar molecular masses.
- Enzymes exhibited a lower optimum pH (4.0) and higher optimum temperature (70°C).
- Specific activity was lower, and proteolytic susceptibility was higher compared to commercial Aspergillus niger phytase.
- Minimal sequence variation was found in the genes, with no correlation to enzyme properties.
- Identical gene sequences encoded enzymes with different pH and temperature optima.
Conclusions:
- Post-translational modifications likely account for variations in pH and temperature optima among A. fumigatus phytases.
- Despite conserved gene sequences, enzyme functionality can differ due to post-translational modifications.
- Further research into post-translational modifications is needed for optimizing phytase applications.
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