상세 정보

underline
Metadata Downloads : dc(xml) or Excel
Cited 0 time in scopus ci

Title 

Enzyme mechanism and catalytic property of β propeller phytase

Authors 

Se Jeong ShinNan Chul HaByung Chul OhTae Kwang OhByung Ha Oh

Publisher 

Elsevier (Cell Press)

Issue Date 

2001

Citation 

Structure, vol. 9, no. 9, pp. 851-858

Keywords 

β propeller phytasecrystal structuredirect phospho-transferenzyme mechanismmetalloenzymephosphatasebacterial enzymephytaseenzyme active siteenzyme activity

Abstract 

Background: Phytases hydrolyze phytic acid (myo-inositol-hexakisphosphate) to less-phosphorylated myo-inositol derivatives and inorganic phosphate. Phytases are used in animal feed to reduce phosphate pollution in the environment. Recently, a thermostable, calcium-dependent Bacillus phytase was identified that represents the first example of the β propeller fold exhibiting phosphatase activity. We sought to delineate the catalytic mechanism and property of this enzyme. Results: The crystal structure of the enzyme in complex with inorganic phosphate reveals that two phosphates and four calcium ions are tightly bound at the active site. Mutation of the residues involved in the calcium chelation results in severe defects in the enzyme's activity. One phosphate ion, chelating all of the four calcium ions, is close to a water molecule bridging two of the bound calcium ions. Fluoride ion, which is expected to replace this water molecule, is an uncompetitive inhibitor of the enzyme. The enzyme is able to hydrolyze any of the six phosphate groups of phytate. Conclusions: The enzyme reaction is likely to proceed through a direct attack of the metal-bridging water molecule on the phosphorous atom of a substrate and the subsequent stabilization of the pentavalent transition state by the bound calcium ions. The enzyme has two phosphate binding sites, the "cleavage site", which is responsible for the hydrolysis of a substrate, and the "affinity site", which increases the binding affinity for substrates containing adjacent phosphate groups. The existence of the two nonequivalent phosphate binding sites explains the puzzling formation of the alternately dephosphorylated myo-inositol triphosphates from phytate and the hydrolysis of myo-inositol monophosphates.

ISSN 

0969-2126

Link 

http://dx.doi.org/10.1016/S0969-2126(01)00637-2

Appears in Collections

1. Journal Articles > Journal Articles

Registered Date

2017-04-19


There are no files associated with this item.
qrcode

FusionCharts.
DSpace Software Coptright(c) 2010 MIT and Hewleft-Packard  /  KRIBB-REPOSITORY ( Email:jakim@kribb.re.kr)