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Journal of Biochemistry Advance Access published online on June 29, 2009
Journal of Biochemistry, doi:10.1093/jb/mvp099
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© The authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Enzymatic characterization and comparison of various Poaceae UDP-GlcA 4-Epimerase Isoforms

Xiaogang Gu1,2, Christopher J Wages2, Kathryn E. Davis2, Paul J. Guyett2 and Maor Bar-Peled1,2,*

1Department of Plant Biology, University of Georgia, Athens, GA 30602-7271, USA
2Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602-4712, USA

*Corresponding author: Maor Bar-Peled, Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602-4712, Telephone: 706-542-4496, Fax: 706-542-4412, E-mail: peled{at}ccrc.uga.edu

Received June 8, 2009; Accepted June 15, 2009


  Abstract

UDP-{alpha}-D galacturonic acid (UDP-GalA) is a key precursor for the synthesis of various bacterial and plant polysaccharides. UDP-glucuronic acid 4-epimerase (UGlcAE) catalyzes the reversible conversion of UDP-{alpha}-D-glucuronic acid to UDP-GalA. UGlcAEs isolated from bacterial species have different biochemical properties when compared with the isoenzymes from the plant dicot species, Arabidopsis. However, little is known about the specificity of UGlcAE in Poaceae species. Therefore, we cloned and expressed in E. coli several maize and rice UGlcAE genes, and compared their enzymatic properties with dicot homologs from Arabidopsis. Our data show that UGlcAE isoforms in different plant species have different enzymatic properties. For example, the Poaceae UGlcAE enzymes from rice and maize have significantly lower Ki for UDP-xylose when compared with the Arabidopsis enzymes. The epimerases from different plant species are very specific and unlike their bacterial homolog in Klebsiella pneumoniae, can only use UDP-GlcA or UDP-GalA as their substrate. This study demonstrates that although members of plant UGlcAE isoforms are highly conserved, the in vitro enzymatic activity of specific Poaceae isoform(s) may be regulated differently by specific nucleotide or nucleotide-sugar.

Key Words: Arabidopsis thaliana, GalA containing glycans, Isoform, Poaceae, UDP-glucuronic acid 4-epimerase


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