Mixed and diverse metabolic and gene-expression regulation of the glycolytic and fermentative pathways in response to aHXK2deletion inSaccharomyces cerevisiae

Abstract

In Saccharomyces cerevisiae the HXK2 gene, which encodes the glycolytic enzyme hexokinase II, is involved in the regulatory mechanism known as 'glucose repression'. Its deletion leads to fully respiratory growth at high glucose concentrations where the wild type ferments profusely. Here we describe that deletion of the HXK2 gene resulted in a 75% reduction in fermentative capacity. Using regulation analysis we found that the fluxes through most glycolytic and fermentative enzymes were regulated cooperatively by changes in their capacities (Vmax) and by changes in the way they interacted with the rest of the metabolism. Glucose transport and phosphofructokinase were regulated purely at the metabolic level. The reduction of fermentative capacity in the mutant was accompanied by a remarkable resilience of the remaining capacity to nutrient starvation. After starvation, the fermentative capacity of the hxk2Delta mutant was similar to that of the wild type. Based on our results and previous reports, we suggest an inverse correlation between glucose repression and the resilience of fermentative capacity towards nutrient starvation. Only a limited number of glycolytic enzyme activities changed upon starvation of the hxk2Delta mutant and we discuss to what extent this could explain the stability of the fermentative capacity.

Effect ofhxk2deletion andHAP4overexpression on fermentative capacity inSaccharomyces cerevisiae

“…Interestingly, TPI activity was much higher than the other glycolytic enzymes. This has been observed by others (Rossell et al , 2008), and could possibly be seen as a mechanism to warrant fast conversion between di‐hidroxyacetone phosphate and glyceraldehyde‐3‐phosphate in order to maintain redox neutrality. When the hxk2 Δ strain was transferred to fermentative conditions with maltose, glycolytic enzyme activity was induced, where the wild‐type activity was decreased after an hour.…”

Metabolic flexibility of a prospective bioremediator: Desulfitobacterium hafniense Y51 challenged in chemostats

“…At the same time, there was a diverse pattern of transcription regulation with many genes significantly regulated. Remarkably, D. hafniense Y51 did not merely adjust its metabolism by re‐tuning transcription of a few genes encoding enzymes with high flux control, nor did it engage in proportional regulation (Rossell et al ., , ); it appeared to re‐tune its metabolism in a variety of more subtle ways.…”

“…Dry weight was measured as previously described (Van Verseveld et al, 1984). Organic acids were measured by HPLC (LC-10AT, Shimadzu, Kyoto, Japan) on a packed Aminex-HPC 87H column (300 × 7.8 mm; Biorad Laboratories, Hercules, CA), and a refractive index detector (RID-10A, Shimadzu, Kyoto, Japan) according to (Rossell et al, 2008). Although chemostat cultivations were carried out under sterile conditions, the purity of D. hafniense Y51 was confirmed microscopically by cultivation on LB agar plates under oxic conditions and by PCR amplification of 16S rRNA gene fragments with generic primers for bacteria followed by Denaturing Gradient Gel Electrophoresis (DGGE), as previously described (Direito et al, 2011).…”

Aspergillus fumigatus Catalytic Glucokinase and Hexokinase: Expression Analysis and Importance for Germination, Growth, and Conidiation

“…In aspergilli this repression system is governed mainly by the DNA-binding protein CreA (15,33), whereas in Saccharomyces cerevisiae Mig1p plays a major role in carbon catabolite repression (21). Studies of S. cerevisiae revealed that the hexokinase Hxk2p additionally participates in the regulation of alternative carbon utilization (23) and fermentative growth in the presence of glucose (39). This regulation appears to be different from that of A. nidulans, in which only the mutation of both glucokinase and hexokinase but not of a single hexose kinase led to derepressed carbon catabolite repression (19).…”