Disease relevance of HXK1

• The complete cry11A region gene of Bacillus thuringiensis ssp. israelensis was fused in frame to the 3' end of the GST gene under the control of the Saccharomyces cerevisiae HXK1 promoter [1].
• Remarkably, the osmotic work of this dehydration would be on the order of only one k T per hexokinase molecule [2].
• We have applied our system to experiments on hexokinase from a variety of sources: yeast, ascites and muscle [3].
• Hexokinase from mouse brain required 50 times higher concentrations for inhibition than the enzyme from mouse Ehrlich ascites tumor cells [4].
• Glycolysis and hexokinase activities in extracts of Rous sarcoma virus transformed cells were considerably more sensitive to the inhibitor than the activities from normal chick embryo fibroblasts [4].

High impact information on HXK1

• Inelastic neutron scattering analysis of hexokinase dynamics and its modification on binding of glucose [5].
• Space-filling models of yeast hexokinase, adenylate kinase, and phosphoglycerate kinase drawn by computer clearly portray the bilobal character of these phosphoryl transfer enzymes, and the deep cleft which is formed between the lobes [6].
• The effects of hexokinase mutations and glucose analogs indicate that this phosphorylation is dependent on glucose phosphorylating activity [7].
• Mixed peptide sequencing identified these proteins as hexokinase II (Hxk2p) and the E1alpha subunit of pyruvate dehydrogenase [8].
• Sequence analysis of a 4-kb genomic clone containing NAG1 indicates that this gene is part of a cluster containing two other genes of the GlcNAc catabolic pathway, i.e., DAC1, GlcNAc-6-phosphate deacetylase, and HXK1, hexokinase [9].

Chemical compound and disease context of HXK1

• The binding of glucose to the enzyme results in significant dehydration of the two interacting molecules, while the intrinsic coefficient of adiabatic compressibility of hexokinase slightly decreases [10].
• An examination of the binding sites of four carbohydrate binding proteins (Escherichia coli lactose repressor, E. coli arabinose-binding protein, yeast hexokinase A and Concanavalin A) revealed certain similarities of amino acid sequences and residues forming hydrogen bonds and hydrophobic interactions with the bound carbohydrate [11].
• Studies on the mechanism of toxicity of metrizamide-competitive inhibition of yeast hexokinase [12].

Biological context of HXK1

• We attempted to expand the substrate spectrum of E. histolytica HXK1 by modifying its active site to become similar to the active site of the fructose phosphorylating yeast hexokinase PII [13].
• We have also studied the induction and repression kinetics of mRNA expression for the HXK1, HXK2 and GLK1 genes [14].
• Differences in substrate specificity and kinetic properties of the recombinant hexokinases HXK1 and HXK2 from Entamoeba histolytica [13].
• Although we cannot rule out a defect in the metabolic state of the cell as the origin of these phenomena, our results suggest that the phosphorylation of hexokinase is essential in vivo for glucose signal transduction [15].
• The mutations were obtained by mutagenesis of cloned HXK2 DNA carried on a low-copy-number plasmid vector and screened for a number of different phenotypes in yeast strains bearing chromosomal hxk1 and hxk2 null mutations [16].

Anatomical context of HXK1

• These findings reveal a novel mechanism of gene regulation whereby the product of a glycolytic gene, normally resident in the cytosol, interacts directly with nuclear proteins to regulate the transcription of the HXK1 and GLK1 genes and to autoregulate its own transcription [17].
• One important feature in order to understand the physiological function of hexokinase PH is that it is a phosphoprotein, since protein phosphorylation is essential in most metabolic signal transductions in eukaryotic cells [15].
• To investigate whether trehalose 6-phosphate (Tre6P) is the sole mediator of hexokinase inhibition, we have reconstituted ethanolic fermentation from glucose in permeabilized spheroplasts of the wild-type, tps1Delta and tps2Delta (Tre6P phosphatase) strains [18].
• A method for determining the intracellular distribution of enzymes in yeast provides no evidence for the association of hexokinase with mitochondria [19].
• No substantial hexokinase activity was found to be associated with cellular organelles [19].

Associations of HXK1 with chemical compounds

• The HXK1 sequence was 76% homologous with that of HXK2, which is responsible for triggering glucose repression in yeasts [20].
• Mannose was phosphorylated well by HXK1, but at a much lower rate by HXK2 [13].
• Expression of hxk1+ increased strongly during growth in fructose or glycerol [21].
• When hex2 mutant cells grown on YEP ethanol were shifted to YEP glucose media, hexokinase activity increased after 30 min [22].
• Hexokinase is the first enzyme in the glycolytic pathway, catalyzing the transfer of a phosphoryl group from ATP to glucose to form glucose 6-phosphate and ADP [23].

Physical interactions of HXK1

• The surface area of the hexokinase A-glucose complex exposed to solvent is smaller than that of native hexokinase B [24].
• Indeed, initiation of Gal2p and FBPase proteolysis appears to require rapid transport of those substrates of the Hxt transporters that are at least partially metabolized by hexokinase Hxk2p [25].
• The actin fold is a structural motif involved in binding of ATP to an otherwise diverse family of proteins that includes hexokinase, actin, and the 70 kDa heat shock protein [26].

Enzymatic interactions of HXK1

• We reduced hexokinase activity in ggs1 strains by deleting the gene HXK2 encoding hexokinase PII [27].

Regulatory relationships of HXK1

• Using the set of six hxk2 mutants it was shown that there is a good correlation between the glucose-induced cAMP signal and in vivo hexokinase activity [28].
• Afterwards, the Tps1-dependent control system is apparently able to restrict properly up to 50-fold higher hexokinase activity [29].
• Phosphofructokinase is inhibited to a greater extent than hexokinase at acid pH [30].

Other interactions of HXK1

• Several hundred new mutations in the gene (HXK2) encoding hexokinase II of Saccharomyces cerevisiae were isolated, and a subset of them was mapped, resulting in a fine-structure genetic map [16].
• Spontaneous revertants of hxk1 hxk2 glk1 strains collected on glucose regain any one of these three enzymes [31].
• Our results show that overexpression of hexokinase does not cause the same phenotype as deletion of Tps1 [29].
• No transcripts of the SUC2 and HXK1 genes, encoding, respectively, invertase and hexokinase isoenzyme 1, could be detected [32].
• Apparently, during the start-up of fermentation hexokinase is more rate-limiting in the first section of glycolysis than phosphofructokinase [29].

Analytical, diagnostic and therapeutic context of HXK1

• Identification, cloning and sequence determination of the genes specifying hexokinase A and B from yeast [33].
• Molecular cloning and characterization of the gene HXK1 encoding the hexokinase from Yarrowia lipolytica [34].
• The change in enthalpy and rate constants for the reactions of yeast hexokinase isozymes, PI (Hxk1) and PII (Hxk2), was determined at pH 7.6 and 25 degrees C by isothermal titration calorimetry [35].
• We show now by site-directed mutagenesis and sedimentation analysis that serine-14 phosphorylation affects the oligomeric state of hexokinase, its substitution by glutamate causing complete dissociation; glutamate exchange for serine-157 does not [36].
• Crystallization and preliminary crystal analysis of yeast hexokinase PI and PII [37].

References