Disease relevance of ICL1

• The ICL1 gene encoding isocitrate lyase was cloned from the dimorphic fungus Yarrowia lipolytica by complementation of a mutation (acuA3) in the structural gene of isocitrate lyase of Escherichia coli [1].
• During this profiling, a single gene for the enzyme isocitrate lyase (ICL1) was found to be up regulated at 1 week of infection in a rabbit meningitis model and during a time of maximum host cellular response [2].
• These findings in fungi, in conjunction with reports that isocitrate lyase is both upregulated and required for the virulence of Mycobacterium tuberculosis, demonstrate the wide-ranging significance of the glyoxylate cycle in microbial pathogenesis [3].
• The ZZ domain derived from Staphylococcus aureus, which binds to the Fc part of immunoglobulin G (IgG), was displayed on the cell surfaces of yeast Saccharomyces cerevisiae by cell-surface engineering using the C-terminal half of alpha-agglutinin under control of the 5'-upstream region of the isocitrate lyase gene from Candida tropicalis (UPR-ICL) [4].

High impact information on ICL1

• The facB gene is required for acetate induction of acetamidase (amdS) and the acetate utilization enzymes acetyl-CoA synthase (facA), isocitrate lyase (acuD) and malate synthase (acuE) in Aspergillus nidulans [5].
• Deletion analysis of the ICL1 promoter led to the identification of an upstream activating sequence element, UASICL1 (5' CATTCATCCG 3'), necessary and sufficient for conferring carbon source-dependent regulation on a heterologous reporter gene [6].
• The GAL82 and GAL83 mutations are probably specific for expression of the Leloir pathway and related enzymes, because they do not affect the synthesis of alpha-D-glucosidase, invertase, or isocitrate lyase [7].
• All mutant strains show in addition a defect in catabolite inactivation of three other gluconeogenic enzymes: cytosolic malate dehydrogenase, isocitrate lyase, and phosphoenolpyruvate carboxykinase [8].
• To investigate acetate and fatty acid utilization, the acuD gene encoding a key glyoxylate cycle enzyme (isocitrate lyase) was cloned [9].

Biological context of ICL1

• Protein binding to UAS1MLS1 was observed with extracts from derepressed but not from repressed cells, and could be competed for by an excess of the unlabelled CSRE (ICL1) sequence [10].
• However, we here demonstrated by in vitro mutagenesis of ICL1 that such an exchange, even though it affects Icl activity to some degree, does not lead to a complete lack of function [11].
• Deletion mutants of UPR-ICL containing only one of these regions showed that each region could independently activate gene expression to a similar level when the cells were grown on acetate [12].
• In this work, we identified an open reading frame 5' to the yeast HALI gene, that shares a 38% identity in the deduced amino acid sequence with gluconeogenic enzyme isocitrate lyase, encoded by ICL1 [11].
• Molecular genetics of ICL2, encoding a non-functional isocitrate lyase in Saccharomyces cerevisiae [11].

Anatomical context of ICL1

• The targeting of castor bean isocitrate lyase to peroxisomes was studied by expression in the heterologous host Saccharomyces cerevisae from which the endogenous ICL1 gene had been removed by gene disruption [13].
• A regulatory factor, Fil1p, involved in derepression of the isocitrate lyase gene in Saccharomyces cerevisiae--a possible mitochondrial protein necessary for protein synthesis in mitochondria [14].
• No peroxisomal remnants were observed inside vacuoles in the cells of acs1, acs2, acs3 and icl1 mutants after prolonged cultivation in ethanol medium [15].
• However, site-directed icl1 mutants had no apparent virulence defect in two animal models and no growth defect within macrophages [2].
• Isocitrate lyase and malate synthase, the two key enzymes of the glyoxylate cycle, were also localized in these organelles [16].

Associations of ICL1 with chemical compounds

• Similar to that of ICL1, transcription of ICL2 is subject to glucose catabolite repression [17].
• A functional glyoxylate cycle is necessary for suppression as a disruption of gene ICL1 encoding isocitrate lyase abolished the phenotypic effect of BPC1-1 on growth in glucose-ammonium [18].
• The Saccharomyces cerevisiae ICL1 gene encodes isocitrate lyase, an essential enzyme for growth on ethanol and acetate [17].
• In the methylcitrate cycle of propionyl-coenzyme A metabolism, 2-methylisocitrate is converted to succinate and pyruvate, a reaction similar to that catalyzed by isocitrate lyase [17].
• Furthermore, cells treated with antimycin A, along with chloramphenicol-treated, rho(o), and deltafil1 cells, showed deficiency in derepression of isocitrate lyase [14].

Physical interactions of ICL1

• The peptide corresponding to wild-type ICL interacted with all three Pex5p proteins to differing extents, but neither mutant could interact with Pex5p from any species [13].

Other interactions of ICL1

• Northern-blot analysis showed that this can be ascribed to no increase in transcription of ICL1 and FBP1 encoding fructose 1,6-bisphosphatase [14].
• Expression of the ICL gene with full-length UPR-ICL increased about tenfold in mig1 cells grown on glucose, while little difference was observed in acetate-grown cells [12].
• By deletion analyses as well as by studying the influence on expression of different fragments cloned into the heterologous CYC1 promoter lacking its own UAS sequences, we defined UAS and URS elements in the ICL1 promoter [19].
• Mutations in gene ICL1, which encodes isocitrate lyase, resulted in overproduction of ACS without any growth on acetate [20].
• The latter is not capable of complementing an icl1 deletion for growth on ethanol neither in its original context, nor when expressed under the control of the glycolytic PFK2 promoter [11].

Analytical, diagnostic and therapeutic context of ICL1

• In Northern blot analyses we first showed that the steady-state ICL1 mRNA levels depend on the carbon source used for growth [19].
• No label was found in the band corresponding to the isocitrate lyase when immunoprecipitation was done with a control pre-immune serum or in the presence of excess pure unlabelled enzyme [21].
• In contrast, mutations T250R-R251N and L255F-K256R located in the C-terminus of the 3rd ICL of AT2 retained ligand-binding properties of the wild-type AT2, and its ability to interact with the ErbB3 in yeast two-hybrid assay, but abolished AT2-mediated cGMP reduction [22].
• We observed subcellular localization of expressed products of the mutant CT-ICL genes by immunoelectron microscopy [23].

References