Cloning and characterization of two genes encoding dihydroxyacetone kinase from Schizosaccharomyces pombe IFO 0354

Ethanol-inducible gene expression using gld1 (+) promoter in the fission yeast Schizosaccharomyces pombe

In the fission yeast Schizosaccharomyces pombe, the gld1 (+) gene encoding glycerol dehydrogenase is repressed by glucose and induced by ethanol and 1-propanol. The promoter region of gld1 (+) was cloned into a multicopy vector designated as pEG1 for evaluation as an ethanol-inducible expression vector using EGFP as a model heterologous protein. Expression of EGFP was repressed in the presence of high glucose and induced in the presence of ethanol, low-glucose, and 1-propanol in the absence of glucose. Addition of ethanol to cells harboring pEG1-EGFP was found to be the most effective means for inducing EGFP production. Protein yields were found to increase in proportion to ethanol concentration. As a further test of effectiveness, secreted recombinant human growth hormone was produced using the pEG1 expression vector in medium containing glycerol and ethanol. The pEG1 gene expression system is an effective tool for the production of heterologous proteins under glucose-limiting conditions, including medium containing glycerol as a carbon source.

The gld1+ gene encoding glycerol dehydrogenase is required for glycerol metabolism in Schizosaccharomyces pombe

The budding yeast Saccharomyces cerevisiae is able to utilize glycerol as the sole carbon source via two pathways (glycerol 3-phosphate pathway and dihydroxyacetone [DHA] pathway). In contrast, the fission yeast Schizosaccharomyces pombe does not grow on media containing glycerol as the sole carbon source. However, in the presence of other carbon sources such as galactose and ethanol, S. pombe could assimilate glycerol and glycerol was preferentially utilized over ethanol and galactose. No equivalent of S. cerevisiae Gcy1/glycerol dehydrogenase has been identified in S. pombe. However, we identified a gene in S. pombe, SPAC13F5.03c (gld1 (+)), that is homologous to bacterial glycerol dehydrogenase. Deletion of gld1 caused a reduction in glycerol dehydrogenase activity and prevented glycerol assimilation. The gld1 Delta cells grew on 50 mM DHA as the sole carbon source, indicating that the glycerol dehydrogenase encoded by gld1 (+) is essential for glycerol assimilation in S. pombe. Strains of S. pombe deleted for dak1 (+) and dak2 (+) encoding DHA kinases could not grow on glycerol and showed sensitivity to a higher concentration of DHA. The dak1 Delta strain showed a more severe reduction of growth on glycerol and DHA than the dak2 Delta strain because the expression of dak1 (+) mRNA was higher than that of dak2 (+). In wild-type S. pombe, expression of the gld1 (+), dak1 (+), and dak2 (+) genes was repressed at a high concentration of glucose and was derepressed during glucose starvation. We found that gld1 (+) was regulated by glucose repression and that it was derepressed in scr1 Delta and tup12 Delta strains.

Glycerol production by microbial fermentation: a review

Microbial production of glycerol has been known for 150 years, and glycerol was produced commercially during World War I. Glycerol production by microbial synthesis subsequently declined since it was unable to compete with chemical synthesis from petrochemical feedstocks due to the low glycerol yields and the difficulty with extraction and purification of glycerol from broth. As the cost of propylene has increased and its availability has decreased especially in developing countries and as glycerol has become an attractive feedstock for production of various chemicals, glycerol production by fermentation has become more attractive as an alternative route. Substantial overproduction of glycerol by yeast from monosaccharides can be obtained by: (1) forming a complex between acetaldehyde and bisulfite ions thereby retarding ethanol production and restoring the redox balance through glycerol synthesis; (2) growing yeast cultures at pH values near 7 or above; or (3) using osmotolerant yeasts. In recent years, significant improvements have been made in the glycerol production using osmotolerant yeasts on a commercial scale in China. The most outstanding achievements include: (1) isolation of novel osmotolerant yeast strains producing up to 130 g/L glycerol with yields up to 63% and the productivities up to 32 g/(L day); (2) glycerol yields, productivities and concentrations in broth up to 58%, 30 g/(L day) and 110-120 g/L, respectively, in an optimized aerobic fermentation process have been attained on a commercial scale; and (3) a carrier distillation technique with a glycerol distillation efficiency greater than 90% has been developed. As glycerol metabolism has become better understood in yeasts, opportunities will arise to construct novel glycerol overproducing microorganisms by metabolic engineering.

Crystal structure of the Citrobacter freundii dihydroxyacetone kinase reveals an eight-stranded alpha-helical barrel ATP-binding domain

Dihydroxyacetone kinases are a sequence-conserved family of enzymes, which utilize two different phosphoryldonors, ATP in animals, plants and some bacteria, and a multiphosphoprotein of the phosphoenolpyruvate carbohydrate phosphotransferase system in bacteria. Here we report the 2.5-A crystal structure of the homodimeric Citrobacter freundii dihydroxyacetone kinase complex with an ATP analogue and dihydroxyacetone. The N-terminal domain consists of two alpha/beta-folds with a molecule of dihydroxyacetone covalently bound in hemiaminal linkage to the N epsilon 2 of His-220. The C-terminal domain consists of a regular eight-helix alpha-barrel. The eight helices form a deep pocket, which includes a tightly bound phospholipid. Only the lipid headgroup protrudes from the surface. The nucleotide is bound on the top of the barrel across from the entrance to the lipid pocket. The phosphate groups are coordinated by two Mg2+ ions to gamma-carboxyl groups of aspartyl residues. The ATP binding site does not contain positively charged or aromatic groups. Paralogues of dihydroxyacetone kinase also occur in association with transcription regulators and proteins of unknown function pointing to biological roles beyond triose metabolism.

Cloning, sequencing and characterization of a gene encoding dihydroxyacetone kinase from Zygosaccharomyces rouxii NRRL2547

The dihydroxyacetone pathway, an alternative pathway for the dissimilation of glycerol via reduction by glycerol dehydrogenase and subsequent phosphorylation by dihydroxyacetone (DHA) kinase, is activated in the yeasts Saccharomyces cerevisiae and Zygosaccharomyces rouxii during osmotic stress. In experiments aimed at investigating the physiological function of the DHA pathway in Z. rouxii, a typical osmotolerant yeast, we cloned and characterized a DAK gene encoding dihydroxyacetone kinase from Z. rouxii NRRL 2547. Sequence analysis revealed a 1761 bp open reading frame, encoding a peptide composed of 587 deduced amino acids with the predicted molecular weight of 61 664 Da. As the amino acid sequence was most closely homologous (68% identity) to the S. cerevisiae Dak1p, we named the gene and protein ZrDAK1 and ZrDak1p, respectively. A putative ATP binding site was also found but no consensus element associated with osmoregulation was found in the upstream region of the ZrDAK1 gene. The ZrDAK1 gene complemented a S. cerevisiae W303-1A dak1delta dak2 delta strain by improving the growth of the mutant on 50 mmol/l dihydroxyacetone and by increasing the tolerance to dihydroxyacetone in a medium containing 5% sodium chloride, suggesting that it is a functional homologue of the S. cerevisiae DAK1. However, expression of the ZrDAK1 gene in the S. cerevisiae dak1delta dak2 delta strain had no significant effect on glycerol levels during osmotic stress. The ZrDAK1 sequence has been deposited in the public data bases under Accession No. AJ294719; regions upstream and downstream of ZrDAK1are deposited as Accession Nos AJ294739 and AJ294720, respectively.

A tomato enzyme catalyzing the phosphorylation of 3,4-dihydroxy-2-butanone

A riboflavin biosynthesis ribB mutant of Escherichia coli deficient of 3,4-dihydroxy-2-butanone 4-phosphate synthase was complemented with a cDNA library from Lycopersicon esculentum. The complementing gene was isolated and expressed in E. coli. The resulting protein was shown to specify a 62 kDa protein which phosphorylates dihydroxyacetone, both enantiomers of 3,4-dihydroxy-2-butanone, and several other aldoses and ketoses. Sequence analysis revealed homology to dihydroacetone kinases (dak) genes from plants, animals, fungi and some eubacteria. Genes with similarity to the 5' part of the dak gene from tomato were found in many other eubacteria. The physiological role of the dak gene is still incompletely known.

Large-scale screening of intracellular protein localization in living fission yeast cells by the use of a GFP-fusion genomic DNA library

BACKGROUND

Intracellular localization is an important part of the characterization of a gene product. In an attempt to search for genes based on the intracellular localization of their products, we constructed a green fluorescent protein (GFP)-fusion genomic DNA library of S. pombe.

RESULTS

We constructed the S. pombe GFP-fusion genomic DNA library by fusing, in all three reading frames, random fragments of genomic DNA to the 5' end of the GFP gene in such a way that expression of potential GFP-fusion proteins would be under the control of the own promoters contained in the genomic DNA fragments. Fission yeast cells were transformed with this plasmid library, and microscopic screening of 49 845 transformants yielded 6954 transformants which exhibited GFP fluorescence, of which 728 transformants showed fluorescence localized to distinct intracellular structures such as the nucleus, the nuclear membrane, and cytoskeletal structures. Plasmids were isolated from 516 of these transformants, and a determination of their DNA sequences identified 250 independent genes. The intracellular localizations of the 250 GFP-fusion constructs was categorized as an image database; using this database, DNA sequences can be searched for based on the localizations of their products.

CONCLUSIONS

A number of new intracellular structural components were found in this library. The library of GFP-fusion constructs also provides useful fluorescent markers for various intracellular structures and cellular activities, which can be readily used for microscopic observation in living cells.