Disease relevance of FBP1

• A natural A/T-rich sequence from the yeast FBP1 gene exists as a cruciform in Escherichia coli cells [1].

High impact information on FBP1

• The key regulatory enzyme in gluconeogenesis, fructose 1,6-bisphosphatase (FBPase) is subject to glucose-stimulated proteolytic degradation in Saccharomyces cerevisiae [2].
• This process involves the regulated transfer of FBPase directly from the cytosol into the vacuole or a vacuole-related organelle [2].
• Here we demonstrate the involvement of Ubc8p in the glucose-induced ubiquitylation of FBPase as a prerequisite for catabolite degradation of the enzyme via the proteasome [3].
• The heat shock protein Ssa2p was identified as one of the ATP binding proteins involved in FBPase import [4].
• The addition of purified recombinant Ssa2p stimulated FBPase import into Deltassa2 Vid vesicles, providing Deltassa2 cytosol was present [4].

Biological context of FBP1

• Analysis of the FBP1 promoter revealed two upstream activating elements, UAS1FBP1 and UAS2FBP1, which confer carbon source-dependent regulation on a heterologous reporter gene [5].
• Regulatory regions in the yeast FBP1 and PCK1 genes [6].
• RT-PCR analysis showed that the expression of the key enzyme in gluconeogenesis fructose-1,6-bisphosphatase (FBP1) was clearly up-regulated by MMS in glucose-rich medium [7].
• Our results indicate that FBP1 influences the connection between DNA damage, aging and oxidative stress through either direct signalling or an intricate adaptation in energy metabolism [7].
• Reintroduction of FBP1 in the knockout restored the wild-type phenotype while overexpression increased MMS sensitivity of wild-type, shortened life span and increased induction of RNR2 after treatment with MMS [7].

Anatomical context of FBP1

• FBPase trafficking to the vacuole involves two distinct steps, import into intermediate transport vesicles (Vid vesicles) and Vid vesicle trafficking to the vacuole [8].
• To identify the required cytosolic component, wild type cytosol was fractionated and screened for proteins that complement Deltavid22 mutant cytosol using an in vitro assay that reproduces FBPase import into Vid vesicles [8].
• Upon glucose addition to yeast cells cultured on nonfermentable carbon sources FBPase is ubiquitinated in vivo [9].
• Vid22p, a novel plasma membrane protein, is required for the fructose-1,6-bisphosphatase degradation pathway [10].
• In contrast to FBPase from yeast or liver, FBPase from skeletal muscle is approximately 1000-fold more sensitive to inhibition by 5' adenosine monophosphate and 30 to 250-fold less sensitive to inhibition by fructose-2,6-bisphosphate [11].

Associations of FBP1 with chemical compounds

• Glucose strongly represses the transcription of the gluconeogenic genes, FBP1 and PCK1, and accelerates the degradation of their mRNAs [12].
• The transcription of the yeast FBP1 and PCK1 genes, which encode the gluconeogenic enzymes fructose-1,6-bisphosphatase and phosphoenolpyruvate carboxykinase, is repressed by glucose [13].
• Interestingly, deletion of FBP1 led to reduced sensitivity to MMS, but not to other DNA-damaging agents, such as 4-NQO or phleomycin [7].
• The cyclosporin A binding pocket is important for Cpr1p function, since cyclosporin A binding-deficient mutants failed to complement FBPase import in Deltacpr1 and Deltavid22 mutants [8].
• Fructose bisphosphatase activity was not greatly overproduced when the FBP1 gene was present on a multicopy vector in yeast [14].

Physical interactions of FBP1

• Regions in the promoter of the yeast FBP1 gene implicated in catabolite repression may bind the product of the regulatory gene MIG1 [15].
• Two of the ORFs code for the well-characterized genes SEC61 (which codes for the core subunit of the ER translocation complex) and FBP1 (encoding fructose-1,6-bisphosphatase) [16].
• A multiubiquitin chain containing isopeptide linkages at Lys48 of ubiquitin is attached to FBPase [9].
• 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 [17].

Enzymatic interactions of FBP1

• Phosphorylated fructose-1,6-bisphosphatase and phosphorylated 6-phosphofructo-2-kinase were present in extracts of starved yeast cells which had been incubated for 10 min with glucose [18].

Regulatory relationships of FBP1

• Neither deletion nor overexpression of the MIG1 gene affected the regulated expression of the FBP1 or PCK1 genes [6].
• A gene cassette was constructed for fructose-1,6-bisphosphatase from S. cerevisiae and the gene cassette expressed from the regulated PHO5 and GAL1 promoters of yeast [19].
• The S. cerevisiae and human SGT1 genes both suppress git7-93 but not git7-235 for glucose repression of fbp1 transcription and benomyl sensitivity [20].
• Furthermore, FBPase import was inhibited when cells overexpressed the K48R/K63R ubiquitin mutant that fails to form multiubiquitin chains [21].
• Otherwise, growth of such strains is indistinguishable from that of RAS2(+) strains. ras2(318S) strains also exhibit a delay in glucose-stimulated phosphorylation and turnover of fructose-1,6-bisphosphatase, a substrate of the cAMP-dependent protein kinase A (PKA) and a key component of the gluconeogenic branch of the glycolytic pathway [22].

Other interactions of FBP1

• The occurrence of Cat8pIII was strongly correlated with the derepression of gluconeogenic enzymes (phosphoenolpyruvate carboxykinase and fructose-1,6-bisphosphatase) and gluconeogenic PCK1 mRNA [23].
• However, VID22 affects FBPase import indirectly through a cytosolic factor [8].
• Furthermore, the addition of purified Cpr1p restored FBPase import in both the Deltacpr1 and the Deltavid22 mutants [8].
• Northern-blot analysis showed that this can be ascribed to no increase in transcription of ICL1 and FBP1 encoding fructose 1,6-bisphosphatase [24].
• Like FBPase, Ubc8p is found in the cytoplasmic fraction of the cell [3].

Analytical, diagnostic and therapeutic context of FBP1

• Catabolite-repression and catabolite-inactivation studies show that, unlike the complete repression of FBP1 mRNA and inactivation of enzyme activity by glucose seen in S. cerevisiae, mRNA levels and enzyme activity of K. lactis Fru(1,6)P2ase decreased only about 2-4-fold due to the presence of glucose in the cell-culture medium [25].
• Southern blot hybridization analysis confirmed the structure of the transplacement and demonstrated that FBP1 is present in single copy in the haploid genome [14].
• Site-directed mutagenesis of the amino-terminal proline residue yielded fructose-1,6-bisphosphatase forms that were no longer degraded via the ubiquitin-proteasome pathway [26].
• Indirect immunofluorescence microscopy studies demonstrate that the imported FBPase is localized to the vacuole in the permeabilized cells [27].
• This was employed to purify the fusion fructose-1,6-bisphosphatase by affinity chromatography [28].

References