Schenk, Gerhard and Elliott, Tristan W. and Leung, Eleanor and Carrington, Lyle E. and Mitic, Natasa and Gahan, Lawrence R. and Guddat, Luke W.
Crystal structures of a purple acid phosphatase, representing
different steps of this enzyme's catalytic cycle.
BMC Structural Biology, 8 (6).
Background: Purple acid phosphatases belong to the family of binuclear metallohydrolases and
are involved in a multitude of biological functions, ranging from bacterial killing and bone
metabolism in animals to phosphate uptake in plants. Due to its role in bone resorption purple acid
phosphatase has evolved into a promising target for the development of anti-osteoporotic
chemotherapeutics. The design of specific and potent inhibitors for this enzyme is aided by detailed
knowledge of its reaction mechanism. However, despite considerable effort in the last 10 years
various aspects of the basic molecular mechanism of action are still not fully understood.
Results: Red kidney bean purple acid phosphatase is a heterovalent enzyme with an Fe(III)Zn(II)
center in the active site. Two new structures with bound sulfate (2.4 Å) and fluoride (2.2 Å) provide
insight into the pre-catalytic phase of its reaction cycle and phosphorolysis. The sulfate-bound
structure illustrates the significance of an extensive hydrogen bonding network in the second
coordination sphere in initial substrate binding and orientation prior to hydrolysis. Importantly,
both metal ions are five-coordinate in this structure, with only one nucleophilic μ-hydroxide
present in the metal-bridging position. The fluoride-bound structure provides visual support for an
activation mechanism for this μ-hydroxide whereby substrate binding induces a shift of this bridging
ligand towards the divalent metal ion, thus increasing its nucleophilicity.
Conclusion: In combination with kinetic, crystallographic and spectroscopic data these structures
of red kidney bean purple acid phosphatase facilitate the proposal of a comprehensive eight-step
model for the catalytic mechanism of purple acid phosphatases in general.
||This article is available from: http://www.biomedcentral.com/1472-6807/8/6 © 2008 Schenk et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
||Crystal structures; purple acid phosphatase; enzymes; catalytic cycle; binuclear metallohydrolases; anti-osteoporotic
||Faculty of Science and Engineering > Chemistry
||16 May 2012 15:14
|Journal or Publication Title:
||BMC Structural Biology
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