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Current Biotechnology

Volume 1 Issue 2
ISSN: 2211-5501
eISSN: 2211-551X


   All Titles

  Galactokinases: Potential Biotechnological Applications as Biocatalysts
  pp.148-154 (7) Authors: Helena Kristiansson, David J. Timson
doi: 10.2174/10148

Galactokinase, a member of the GHMP (galactokinase, homoserine kinase, mevalonate kinase, phosphomevalonate kinase) family of kinases, catalyses the ATP-dependent phosphorylation of galactose at position 1 on the sugar. This reaction is important in the Leloir pathway of galactose catabolism. The need to produce monosaccharides phosphorylated at position 1 for the synthesis of complex molecules, including aminoglycoside antibiotics, has stimulated interest in exploiting the catalytic potential of galactokinases. However, the enzyme is quite specific, generally only catalysing the phosphorylation of D-galactose and closely related molecules. Directed evolution strategies have identified a key tyrosine residue (Tyr-371 in the Escherichia coli enzyme) which, although distant from the active site, influences the specificity of the enzyme. Alteration of this residue to histidine in E. coli and Lactococcus lactis galactokinases dramatically expanded the substrate range to include both D- and L-sugars. Similar experiments with the human enzyme demonstrated that alteration of the equivalent tyrosine (Tyr-379) to cysteine, lysine, arginine, serine or tryptophan increased the catalytic promiscuity of the enzyme. It has been hypothesised that these specificity changes arise because of alterations in the flexibility of the polypeptide chain. This hypothesis has yet to be tested experimentally. The biotechnological potential of galactokinases is clearly considerable and exploitation of closely related enzymes such as Nacetylgalactosamine kinase and arabinose kinase would expand that potential still further.

  Keywords: Galactokinase, N-acetylgalactosamine kinase, Sugar 1-phosphate, in vitro glycorandomisation, enzyme engineering, protein flexibility, homoserine kinase, mevalonate kinase, phosphomevalonate kinase, Pyrococcus furiosus, Lactococcus lactis, MONOSACCHARIDE 1-PHOSPHATES, L-arabinose, D-galactose, glycorandomization
  Affiliation: School of BiologicalSciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast, BT9 7BL, UK.
  Key: New Content Free Content Open Access Plus Subscribed Content

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