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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 30, Number 6
BKCSDE 30(6)
June 20, 2009 

 
Title
Cloning, Expression, and Characterization of UDP-glucose Pyrophosphorylase from Sphingomonas chungbukensis DJ77
Author
Moon Young Yoon, Kyoung jin Lee, Hea Chul Park, Sung Ha Park, Sang Gon Kim, Sung Kun Kim, Jung Do Choi*
Keywords
UDP-glucose pyrophosphorylase, Sphingomonas chungbukensis, Extracellular polysaccharide, Site-directed mutagenesis
Abstract
The bacterium Sphingomonas chungbukensis DJ77 produces the extracellular polysaccharide gellan in high yield. Gellan produced by this bacterium is widely used as a gelling agent, and the enzyme UDP-glucose pyrophosphorylase (UGP) is thought to play a key role in the gellan biosynthetic pathway. The UGP gene has been successfully cloned and over-expressed in E. coli. The expressed enzyme was purified with a molecular weight of approximately 32 kDa, as determined by a SDS-polyacrylamide gel, but the enzyme appears as ca. 63 kDa on a native gel, suggesting that the enzyme is present in a homodimer. Kinetic analysis of UDP-glucose for UGP indicates Km = 1.14 mM and Vmax = 10.09 mM/min/mg at pH 8.0, which was determined to be the optimal pH for UGP catalytic activity. Amino acid sequence alignment against other bacteria suggests that the UGP contains two conserved domains: An activator binding site and a glucose-1-phosphate binding site. Site-directed mutagenesis of Lys194, located within the glucose-1-phosphate binding site, indicates that substitution of the charge-reversible residue Asp for Lys194 dramatically impairs the UGP activity, supporting the hypothesis that Lys194 plays a critical role in the catalysis.
Page
1360 - 1364
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