Functional cloning and characterization of a UDP- glucuronic acid decarboxylase: The pathogenic fungus Cryptococcus neoformans elucidates UDP-xylose synthesis

doi:10.1073/pnas.211229198

Functional cloning and characterization of a UDP- glucuronic acid decarboxylase: The pathogenic fungus Cryptococcus neoformans elucidates UDP-xylose synthesis

^*Complex Carbohydrate Research Center and Department of Botany, University of Georgia, Athens, GA 30602; and ^‡Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110

Edited by Saul Roseman, The Johns Hopkins University, Baltimore, MD, and approved August 7, 2001 (received for review May 8, 2001)

Abstract

UDP-xylose is a sugar donor required for the synthesis of diverse and important glycan structures in animals, plants, fungi, and bacteria. Xylose-containing glycans are particularly abundant in plants and in the polysaccharide capsule that is the major virulence factor of the pathogenic fungus Cryptococcus neoformans. Biosynthesis of UDP-xylose is mediated by UDP-glucuronic acid decarboxylase, which converts UDP-glucuronic acid to UDP-xylose. Although this enzymatic activity was described over 40 years ago it has never been fully purified, and the gene encoding it has not been identified. We used homology to a bacterial gene, hypothesized to encode a related function, to identify a cryptococcal sequence as putatively encoding a UDP-glucuronic acid decarboxylase. A soluble 47-kDa protein derived from bacteria expressing the C. neoformans gene catalyzed conversion of UDP-glucuronic acid to UDP-xylose, as confirmed by NMR analysis. NADH, UDP, and UDP-xylose inhibit the activity. Close homologs of the cryptococcal gene, which we termed UXS1, appear in genome sequence data from organisms ranging from bacteria to humans.

Footnotes

↵ † To whom reprint requests should be addressed. E-mail: peled{at}ccrc.uga.edu or doering{at}borcim.wustl.edu.
This paper was submitted directly (Track II) to the PNAS office.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF385328).
↵ § De Souza Gutierrez, A. L., Heise, N., Wait, R., Jones, C., Previato, J. O. & Mendonca-Previato, L. (1999) Glycobiology, 9, 1114 (abstr.).