title: Galactokinase promiscuity: a question of flexibility?
abstract: Galactokinase catalyses the first committed step of the Leloir pathway, i.e. the ATP-dependent phosphorylation of α-D-galactose at C1-OH. Reduced galactokinase activity results in the inherited metabolic disease type II galactosaemia. However, inhibition of galactokinase is considered a viable approach to treating more severe forms of galactosaemia (types I and III). Considerable progress has been made in the identification of high affinity, selective inhibitors. Although the structure of galactokinase from a variety of species is known, its catalytic mechanism remains uncertain. Although the bulk of evidence suggests that the reaction proceeds via an active site base mechanism, some experimental and theoretical studies contradict this. The enzyme has potential as a biocatalyst in the production of sugar 1-phosphates. This potential is limited by its high specificity. A variety of approaches have been taken to identify galactokinase variants which are more promiscuous. These have broadened galactokinase's specificity to include a wide range of D- and L-sugars. Initial studies suggest that some of these alterations result in increased flexibility at the active site. It is suggested that modulation of protein flexibility is at least as important as structural modifications in determining the success or failure of enzyme engineering.
authors: School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL. U.K.
authors: Megan
authors: M
authors: McAuley
authors: School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL. U.K.
authors: Helena
authors: H
authors: Kristiansson
authors: School of Chemistry and Chemical Engineering, Queen's University, Belfast, David Kier Building, Stranmillis Road, Belfast BT9 5AG. U.K.
authors: Meilan
authors: M
authors: Huang
authors: Department of Physical Chemistry, Faculty of Sciences, University of Granada, Av. Fuentenueva s/n, Granada 18071, Spain.
authors: Angel L
authors: AL
authors: Pey
authors: School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL. U.K. School of Pharmacy and Biomolecular Sciences, University of Brighton, Huxley Building, Lewes Road, Brighton BN2 4GJ, U.K. d.timson@brighton.ac.uk.
authors: David J
authors: DJ
authors: Timson
mesh_terms: D000818:Animals; D001709:Biotechnology; D005686:Galactokinase / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism*; D005693:Galactosemias / Q000201:enzymology; D006801:Humans; D013379:Substrate Specificity
chemical_list: D005686:Galactokinase
keywords: GHMP kinase; enzyme engineering; enzyme mechanism; galactosaemia; galactose; specificity