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Glycobiology Advance Access originally published online on December 20, 2006
Glycobiology 2007 17(3):345-354; doi:10.1093/glycob/cwl081
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© The Author 2006. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

A plant mutase that interconverts UDP-arabinofuranose and UDP-arabinopyranose

Teruko Konishi2,3, Takumi Takeda4, Yasumasa Miyazaki3, Mayumi Ohnishi-Kameyama5, Takahisa Hayashi4, Malcolm A. O'Neill6 and Tadashi Ishii1,3

3 Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, 305-8687, Japan
4 Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto, 611-0011, Japan
5 National Food Research Institute, Tsukuba, Ibaraki, 305-8642, Japan
6 Complex Carbohydrate Research Center, The University of Georgia, Athens, GA 30602

1 To whom correspondence should be addressed; e-mail: tishii{at}ffpri.affrc.go.jp

Received on November 28, 2006; revised on December 15, 2006; accepted on December 17, 2006

Plant cell walls constitute the bulk of the earth renewable source of energy and are a component in the diet of humans and herbivores. L-Arabinofuranosyl (Araf) residues are a quantifiably important constituent of these walls. Plants use uridine diphosphate (UDP)-L-arabinofuranose (UDP-Araf) to donate Araf residues in the biosynthesis of Araf-containing polysaccharides, proteoglycans, and glycoproteins. However, little is known about the formation of UDP-Araf. We now describe the purification and partial characterization of a rice UDP-arabinopyranose mutase (UAM) that catalyzes the formation of UDP-Araf from UDP-arabinopyranose (UDP-Arap). The reaction is reversible and at thermodynamic equilibrium the pyranose form is favored over the furanose form (90 : 10). Three related proteins that are encoded by rice gene loci Os03g40270, Os04g56520, and Os07g41360 were identified from partial amino acid sequences of UAM. These proteins have >80% sequence identity with polypeptides that are reversibly glycosylated in the presence of UDP-sugars. The rice mutase and two functionally active recombinant mutases were shown to be reversibly glycosylated in the presence of UDP-Glc. The cofactor, flavin-adenine-dinucleotide (FAD), is required for the catalytic activity of UDP-galactose mutases of prokaryotes, fungi, and protozoa. The plant mutases, which do not require a cofactor, must therefore have a different catalytic mechanism. Putative UAM-encoding genes are present in the green algae Chlamydomonas reinhardtii, the moss Physcomitrella patens, the gymnosperm Pinus taeda (loblolly pine), and in numerous dicots and monocots, indicating that UAMs are widespread in green plants.

Key words: arabinofuranose / reversibly glycosylated polypeptide / UDP-arabinopyranose mutase

2 Present address: Department of Bioscience and Biotechnology, University of the Ryukyus, Nishihara, Okinawa, 903-0213, Japan.


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