The unique hexokinase of Kluyveromyces lactis - Molecular and functional characterization and evaluation of a role in glucose signaling

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Item Type:	Article
Title:	The unique hexokinase of Kluyveromyces lactis - Molecular and functional characterization and evaluation of a role in glucose signaling
Creators Name:	Baer, D., Golbik, R., Huebner, G., Lilie, H., Mueller, E.C., Naumann, M., Otto, A., Reuter, R., Breunig, K.D. and Kriegel, T.M.
Abstract:	The Crabtree-negative yeast Kluyveromyces lactis is capable of adjusting its glycolytic flux to the requirements of respiration by tightly regulating glucose uptake. RAG5 encoding the only glucose and fructose phosphorylating enzyme present in K. lactis is required for the up-regulation of glucose transport and also for glucose repression. To understand the significance of the molecular identity and specific function(s) of the corresponding kinase to glucose signaling, RAG5 was overexpressed and its gene product KlHxk1 (Rag5p) isolated and characterized. Stopped-flow kinetics and sedimentation analysis indicated a monomer-homodimer equilibrium of KlHxk1 in a condition of catalysis, i.e. in the presence of substrates and products. The kinetic constants of ATP-dependent glucose phosphorylation identified a 53-kDa monomer as the high affinity/high activity form of the novel enzyme for both glycolytic substrates suggesting a control of glucose phosphorylation at the level of dimer formation and dissociation. In contrast to the highly homologous hexokinase isoenzyme 2 of Saccharomyces cerevisiae (ScHxk2), KlHxk1 was not inhibited by free ATP in a physiological range of nucleotide concentration. Mass spectrometric sequencing of tryptic peptides of KlHxk1 identified unmodified serine at amino acid position 156. The corresponding amino acid in ScHxk2 is serine 157, which represents the autophosphorylation-inactivation site. KlHxk1 did not display, however, the typical pattern of inactivation under the respective in vitro conditions and maintained a high residual glucose phosphorylating activity. The biophysical and functional data are discussed with respect to a possible regulatory role of KlHxk1 in glucose metabolism and signaling in K. lactis.
Keywords:	Amino Acid Sequence, Catalytic Domain, Fungal Genes, Glucose, Hexokinase, Isoenzymes, Kinetics, Kluyveromyces, Molecular Sequence Data, Quaternary Protein Structure, Recombinant Proteins, Serine, Signal Transduction
Source:	Journal of Biological Chemistry
ISSN:	0021-9258
Publisher:	American Society for Biochemistry and Molecular Biology
Volume:	278
Number:	41
Page Range:	39280-39286
Date:	10 October 2003
Official Publication:	https://doi.org/10.1074/jbc.M305706200
PubMed:	View item in PubMed

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