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Metal-Ion Mutagenesis: Conversion of a Purple Acid Phosphatase from Sweet Potato to a Neutral Phosphatase with the Formation of an Unprecedented Catalytically Competent MnIIMnII Active Site

Mitic, Natasa and Noble, Christopher J. and Gahan, Lawrence R. and Hanson, Graeme R. and Schenk, Gerhard (2009) Metal-Ion Mutagenesis: Conversion of a Purple Acid Phosphatase from Sweet Potato to a Neutral Phosphatase with the Formation of an Unprecedented Catalytically Competent MnIIMnII Active Site. Journal of the American Chemical Society, 131 (23). pp. 8173-8179. ISSN 0002-7863

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Abstract

The currently accepted paradigm is that the purple acid phosphatases (PAPs) require a heterovalent, dinuclear metal-ion center for catalysis. It is believed that this is an essential feature for these enzymes in order for them to operate under acidic conditions. A PAP from sweet potato is unusual in that it appears to have a specific requirement for manganese, forming a unique FeIII-μ-(O)-MnII center under catalytically optimal conditions (Schenk et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 273). Herein, we demonstrate, with detailed electron paramagnetic resonance (EPR) spectroscopic and kinetic studies, that in this enzyme the chromophoric FeIII can be replaced by MnII, forming a catalytically active, unprecedented antiferromagnetically coupled homodivalent MnII-μ-(H)OH-μ-carboxylato-MnII center in a PAP. However, although the enzyme is still active, it no longer functions as an acid phosphatase, having optimal activity at neutral pH. Thus, PAPs may have evolved from distantly related divalent dinuclear metallohydrolases that operate under pH neutral conditions by stabilization of a trivalent-divalent metal-ion core. The present MnII-MnII system models these distant relatives, and the results herein make a significant contribution to our understanding of the role of the chromophoric metal ion as an activator of the nucleophile. In addition, the detailed analysis of strain broadened EPR spectra from exchange-coupled dinuclear MnII-MnII centers described herein provides the basis for the full interpretation of the EPR spectra from other dinuclear Mn metalloenzymes.

Item Type: Article
Additional Information: The definitive version of this article was published in the Journal of the American Chemical Society, 2009, 131 (23), pp 8173–8179, DOI: 10.1021/ja900797u . Copyright © 2009 American Chemical Society
Keywords: Metal-Ion; Mutagenesis; Conversion; Purple Acid Phosphatase; Sweet Potato; Neutral Phosphatase; Formation; Unprecedented Catalytically Competent; MnIIMnII Active Site;
Subjects: Science & Engineering > Chemistry
Item ID: 3699
Depositing User: Gary Schenk
Date Deposited: 29 May 2012 15:30
Journal or Publication Title: Journal of the American Chemical Society
Publisher: American Chemical Society
Refereed: Yes
URI:

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