PHYA GENE PRODUCT OF ASPERGILLUS FICUUM AND PENIOPHORA LYCII PRODUCES TWO DISSIMILAR PHYTASES

Authors: Ullah, Abul; Sethumadhavan, Kandan

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2003
Publication Date: 4/4/2003
Citation: Ullah, A.H., Sethumadhavan, K. 2003. Phya gene product of aspergillus ficuum and peniophora lycii produces two dissimilar phytases. Biochemical and Biophysical Research Communications. 303(2):463-468.

Interpretive Summary: The anti-nutritive compound, phytic acid, is copiously present in soybean and other legume seeds. It interferes with the mineral nutrition in one-stomached animals such as chicken, pig, and humans because they lack the enzyme, phytase, needed for breaking down this compound. The undigested phytic acid in the excreta also creates an environmental problem by putting too much phosphate compound in the ground water due to its degradation by the microbes such as fungi, which have active enzyme for degrading phytic acid. To combat this environmental problem we have developed a fungal enzyme through recombinant technology. This enzyme is now produced in Europe and marketed throughout the world. A second enzyme from another fungal group was also developed by a competing firm. In this paper we reported a comparative analysis of the properties of these two different enzymes. While phytase from Aspergillus species is more stable than the other enzyme, it has considerably less activity. However, the active phytase from Peniophora species is comparatively less stable than the enzyme produced by Aspergillus species. The differences between the enzymatic properties of these two important phytases point clearly that there is no one enzyme that is superior. Genetic modification of the Aspergillus enzyme to make it more active may be one way to combat this problem. An active and stable phytase will have a wide application to reduce not only phosphate pollution in our groundwater but also make the soybean meal and other legume a better feed by degrading phytic acid that is present in the meal.

Technical Abstract: PhyA gene product of Aspergillus ficuum (AF) and Peniophora lycii (PL) as expressed in industrial strains of Aspergillus niger and Aspergillus oryzae, respectively, were purified to homogeneity and then characterized for both physical and biochemical properties. The PL phytase is 26 amino acid residues shorter than the AF phytase. Dynamic light scattering studies indicate that the active AF phytase is a monomer while the PL phytase is a dimer. While both of the phytases retained four identical glycosylatable Asn residues, unique glycosylation sites, six for PL and seven for AF phytase, were observed. Global alignment of both the phytases have shown 38% sequence homology between the two proteins. At 58ºC and pH 5.0, the PL phytase gave a specific activity of 22,000 nKat/mg as opposed to about 3,000 nKat/mg for AF phytase. However, the AF phytase is more thermostable than its counterpart PL phytase at 65ºC. Also, AF phytase is more stable at pH 7.5 than the PL phytase. The two phytases differed in Km for phytate, Ki for myo-inositol hexasulfate (MIHS), and pH optima profile. Despite similarities in the active site sequences, the two phytases show remarkable differences in turnover number, pH optima profile, stability at higher temperature, and alkaline pH. These biochemical differences indicate that phytases from ascomycete and basidiomycete fungi may have evolved to degrade phytate in different environment.