1
Department of Life Science and School of Environmental
Engineering, Pohang University of Science and Technology, Pohang,
Kyungbuk, 790-784, South Korea.
2
Microbial enzyme RU, Korea Research Institute of Bioscience
& Biotechnology, P.O. Box 115, Yusong, Taejon
305-600, South Korea.
3
Center for TARA, University of Tsukuba,
305 Tsukuba, Japan.
Phytases hydrolyze phytic acid to less phosphorylated myo-inositol
derivatives and inorganic phosphate. A thermostable phytase is of great value
in applications for improving phosphate and metal ion availability in animal
feed, and thereby reducing phosphate pollution to the environment. Here, we
report a new folding architecture of a six-bladed propeller for phosphatase
activity revealed by the 2.1 Å crystal structures of a novel, thermostable
phytase determined in both the partially and fully Ca2+-loaded
states. Binding of two calcium ions to high-affinity calcium binding sites
results in a dramatic increase in thermostability (by as much as 30°C
in melting temperature) by joining loop segments remote in the amino acid
sequence. Binding of three additional calcium ions to low-affinity calcium
binding sites at the top of the molecule turns on the catalytic activity of
the enzyme by converting the highly negatively charged cleft into a favorable
environment for the binding of phytate.
30°C
in melting temperature) by joining loop segments remote in the amino acid
sequence. Binding of three additional calcium ions to low-affinity calcium
binding sites at the top of the molecule turns on the catalytic activity of
the enzyme by converting the highly negatively charged cleft into a favorable
environment for the binding of phytate.
