Location: Commodity Utilization Research
Title: Conservation of Cysteine Residues in Fungal Histidine Acid Phytases Authors
Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 27, 2004
Publication Date: March 11, 2005
Citation: Mullaney, E.J., Ullah, A.H., 2005. Conservation of cysteine residues in fungal histidine acid phytases. Biochemical and Biophysical Research Communications. Biochemical and Biophysical Research Communications. 328(2):404-408. Interpretive Summary: Today one of the most promising means to reduce levels of phosphorus in swine and poultry manure is the use of a special feed additive, phytase. Water run off from manure with high levels of phosphorus can cause fish kills in our waterways. Phytase helps animals digest a form of phosphorus, phytate, found in many seeds and meals that are used in animal feed. A more complete digestion of this phytate means healthier animals and less phosphorus in their manure. This study confirmed the widespread importance of a structural component of phytase, disulfide bridges. These bonds help the enzyme to maintain its proper shape and thus its activity. The phytases with higher stability have an extra set of these bonds. Knowledge based technology is now being employed to engineer a phytase with higher stability and heat tolerance to further this enzyme's use in animal feed. This study shows that disulfide bonds must be conserved or enhanced to achieve this objective.
Technical Abstract: Amino acid sequence analysis of fungal histidine acid phosphatases displaying phytase activity has revealed a conserved eight-cysteine motif. These conserved amino acids are not directly associated with catalytic function; rather they appear to be essential in the formation of disulfide bridges. Their role is seen as being similar to another eight-cysteine motif recently reported in the amino acid sequence of nearly 500 plant polypeptides. An additional disulfide bridge formed by two cysteines at the N-terminus of all the filamentous ascomycete phytases was also observed. Disulfide bridges are known to increase both stability and heat tolerance in proteins. It is therefore plausible that this extra disulfide bridge contributes to the higher stability found in phytase from some Aspergillus species. To engineer an enhanced phytase for the feed industry, it is imperative that the role of disulfide bridges be taken into cognizance and possibly be increased in number to further elevate stability in this enzyme.