An Unusual Hexose-ATP-Kinase with Two Catalytic Sites and a Role in Carbon Catabolite Repression in the Yeast Schwanniomyces occidentalis

McCann, A. Kate; Hilberg, Frank; Kenworthy, P.; Barnett, James A.

doi:10.1099/00221287-133-2-381

Cited by 9 publications

(8 citation statements)

References 44 publications

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“…The latter is corroborated by the fact that they actually found two protein bands with similar molecular mass after SDSRAGE of their preparation. A similar case has recently been reported for the yeast Schwanninmyces occidentalis (McCann et al, 1987 ;Rose, 1995).…”

Section: Discussionsupporting

confidence: 82%

Cloning and Biochemical Characterisation of an Aspergillus Niger Glucokinase

Panneman

Ruijter

Broeck

et al. 1996

European Journal of Biochemistry

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The Aspergillus niger glucokinase gene glkA has been cloned using a probe generated by polymerase chain reaction with degenerate oligonucleotides. The DNA sequence of the gene was determined, and the deduced amino acid sequence shows significant similarity to other eukaryotic hexokinase and glucokinase proteins, in particular to the Saccharomyces cerevisiae glucokinase protein. The encoded protein was purified from a multicopy glkA transformant, and extensively characterised. The protein has a molecular mass of 54536 Da and a PI of 5.2. The enzyme has high affinity for glucose (K, 0.063 mM at pH 7.5) and a relatively low affinity for fructose (K, 120 mM at pH 7.5), and in vivo fructose phosphorylation by glucokinase is consequently negligible. The configurations at C1 and C4 of the substrate appear to be essential for substrate specificity. The A. niger glucokinase shows non-competitive inhibition by ADP towards ATP and uncompetitive inhibition by ADP towards glucose. The k,,, (turnover number) decreases rapidly below pH 7.5 (56% at pH 7.0 and 17% at pH 6.5) and this may have important implications for the in vivo regulation of activity. In addition, proof is provided for the presence of a second hexosephosphorylating enzyme in A. niger. This enzyme is probably a hexokinase, since unlike glucokinase, this activity is inhibited by trehalose 6-phosphate.

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Section: Discussionsupporting

confidence: 82%

Cloning and Biochemical Characterisation of an Aspergillus Niger Glucokinase

Panneman

Ruijter

Broeck

et al. 1996

European Journal of Biochemistry

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“…This is, to our knowledge, a unique situation. In Schwanniomyces occidentalis, a single enzyme for both hexokinase and glucokinase activities has been postulated (33), but in the absence of genetic analysis, it is not known whether these activities correspond to a single gene.…”

Section: Discussionmentioning

confidence: 99%

The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

Prior¹,

Mamessier²,

Fukuhara³

et al. 1993

Mol. Cell. Biol.

104

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The R4GI gene of Kluyveromyces lactis encodes a low-affinity glucose/fructose transporter. Its transcription is induced by glucose, fructose, and several other sugars. The RAG4, RAGS, and RAG8 genes are trans-acting genes controlling the expression of the RAG) gene. We report here the characterization of one of these genes, RAG5. The nucleotide sequence of the cloned RAGS gene indicated that it encodes a protein that is homologous to hexokinases of Saccharomyces cerevisiae. ragS mutants showed no detectable hexokinase or glucokinase activity, suggesting that the sugar kinase activity encoded by this gene is the only hexokinase in K. lactis. Both high-and low-affinity transport systems of glucose were affected in ragS mutants. The defect of the low-affinity component was found to be due to a block of transcription of the RAG) gene by the hexokinase mutation. In vivo complementation of the rag5 mutation by the K2 gene of S. cerevisiae and complementation of hxikl hxk2 mutations of S. cerevisiae by the RAGS gene showed that RAGS and HXK2 were equivalent for sugar-phosphorylating activity but that RA4GS could not restore glucose repression in the S. cerevisiae hexokinase mutants.

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“…In contrast, in a similar experiment, Hxk1 from Y. lipolytica was fully effective (Petit & Gancedo, 1999) and there is preliminary evidence that Yl Hxk1 is involved in glucose repression of the LIP2 gene encoding an extracellular lipase in Y. lipolytica (Fickers et al , 2005). It has also been reported that in mutants of Schwanniomyces occidentalis or Pachysolen tannophilus , which lack a specific isoenzyme of hexokinase, glucose repression is defective (McCann et al , 1987; Wedlock & Thornton, 1989).…”

Section: Sensing Elementsmentioning

confidence: 99%

The early steps of glucose signalling in yeast

2008

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In the presence of glucose, yeast undergoes an important remodelling of its metabolism. There are changes in the concentration of intracellular metabolites and in the stability of proteins and mRNAs; modifications occur in the activity of enzymes as well as in the rate of transcription of a large number of genes, some of the genes being induced while others are repressed. Diverse combinations of input signals are required for glucose regulation of gene expression and of other cellular processes. This review focuses on the early elements in glucose signalling and discusses their relevance for the regulation of specific processes. Glucose sensing involves the plasma membrane proteins Snf3, Rgt2 and Gpr1 and the glucose-phosphorylating enzyme Hxk2, as well as other regulatory elements whose functions are still incompletely understood. The similarities and differences in the way in which yeasts and mammalian cells respond to glucose are also examined. It is shown that in Saccharomyces cerevisiae, sensing systems for other nutrients share some of the characteristics of the glucose-sensing pathways.

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An Unusual Hexose-ATP-Kinase with Two Catalytic Sites and a Role in Carbon Catabolite Repression in the Yeast Schwanniomyces occidentalis

Cited by 9 publications

References 44 publications

Cloning and Biochemical Characterisation of an Aspergillus Niger Glucokinase

Cloning and Biochemical Characterisation of an Aspergillus Niger Glucokinase

The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

The early steps of glucose signalling in yeast

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