guanosine-diphosphate-mannose and fructose-6-phosphate

Phosphomannose isomerase (PMI40) catalyzes the conversion between fructose 6-phosphate and mannose 6-phosphate and thus connects glycolysis, i.e. energy production and GDP-mannose biosynthesis or cell wall synthesis in Saccharomyces cerevisiae. After PMI40 deletion (pmi(-)) the cells were viable only if fed with extracellular mannose and glucose. In an attempt to force the GDP-mannose synthesis in the pmi(-) strain by increasing the extracellular mannose concentrations, the cells showed significantly reduced growth rates without any alterations in the intracellular GDP-mannose levels. To reveal the mechanisms resulting in reduced growth rates, we measured genome-wide gene expression levels, several metabolite concentrations, and selected in vitro enzyme activities in central metabolic pathways. The increasing of the initial mannose concentration led to an increase in the mannose 6-phosphate concentration, which inhibited the activity of the second enzyme in glycolysis, i.e. phosphoglucose isomerase converting glucose 6-phosphate to fructose 6-phosphate. As a result of this limitation, the flux through glycolysis was decreased as was the median expression of the genes involved in glycolysis. The expression levels of RAP1, a transcription factor involved in the regulation of the mRNA levels of several enzymes in glycolysis, as well as those of cell cycle regulators CDC28 and CLN3, decreased concomitantly with the growth rates and expression of many genes encoding for enzymes in glycolysis.

Topics: Allosteric Site; Bioreactors; CDC28 Protein Kinase, S cerevisiae; Cyclins; Dose-Response Relationship, Drug; Fructosephosphates; Gene Deletion; Gene Expression Regulation; Gene Expression Regulation, Fungal; Genome, Fungal; Glucose; Glucose-6-Phosphate; Glucose-6-Phosphate Isomerase; Glycolysis; Guanosine Diphosphate Mannose; Mannose; Mannose-6-Phosphate Isomerase; Models, Biological; Phosphofructokinases; Protein Processing, Post-Translational; RNA, Messenger; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Shelterin Complex; Telomere-Binding Proteins; Time Factors; Transcription Factors

In this report a recombinant bifunctional phosphomannose isomerase/GDP-D-mannose pyrophosphorylase from Helicobacter pylori has been studied. The enzyme catalyzes the first and third steps of GDP-D-mannose biosynthesis from D-fructose-6-phosphate. The first step, isomerization from D-fructose-6-phosphate to D-mannose-6-phosphate, is found to be rate-limiting in GDP-D-mannose biosynthesis due to feedback inhibition. The inhibition is of non-competitive (mixed) type. As the enzyme is found only in bacteria probably participating in capsular polysaccharide biosynthesis, it could be a specific therapeutic target against bacterial infection.

Topics: Bacterial Proteins; Conserved Sequence; Enzyme Activation; Feedback, Physiological; Fructosephosphates; Guanosine Diphosphate Mannose; Helicobacter pylori; Mannose-6-Phosphate Isomerase; Mannosephosphates; Molecular Sequence Data; Multienzyme Complexes; Nucleotidyltransferases; Recombinant Proteins; Sequence Homology, Amino Acid