Glucose sensing through the Hxk2-dependent signalling pathway

Abstract

In this work, we describe the hexokinase 2 (Hxk2) signalling pathway within the yeast cell. Hxk2 and Mig1 are the two major factors of glucose repression in Saccharomyces cerevisiae. The functions of both proteins have been extensively studied but there is no information about possible interactions among them in the repression pathway. Our results demonstrate that Hxk2 interacts directly with Mig1 in vivo and in vitro and that the ten amino acids motif between K6 and M15 is required for their interaction. This interaction has been detected at the DNA level both in vivo by chromatin immunoprecipitation experiments and in vitro using purified proteins and a DNA fragment containing the MIG1 site of the SUC2 promoter. This demonstrates that the interaction is of physiological relevance. Our findings show that the main role of Hxk2 in the glucose signalling pathway is the interaction with Mig1 to generate a repressor complex located in the nucleus of S. cerevisiae.

Hexokinase 2 Is an Intracellular Glucose Sensor of Yeast Cells That Maintains the Structure and Activity of Mig1 Protein Repressor Complex

“…In high glucose conditions, the repressor protein Mig1 is the main transcription factor responsible for the repression of genes needed for utilization of alternative fermentable carbon sources (7,12). Mig1 binds to DNA and inhibits transcription of SUC2, plus ϳ350 other genes (13,14), but it has been demonstrated that in several cases this process also requires the Hxk2 protein (15)(16)(17). Expression of the HXK2 gene is controlled by glucose availability and is mediated by the Rgt1 and Med8 transcription factors, which repress HXK2 expression in low-glucose-containing media (18,19).…”

Crystal Structure of Hexokinase KlHxk1 of Kluyveromyces lactis

“…In particular, the structure of the symmetrical KlHxk1 dimer serves to explain why phosphorylation of conserved residue Ser-15 may cause electrostatic repulsions with nearby negatively charged residues of the adjacent subunit, thereby inducing a dissociation of the homologous dimeric hexokinases KlHxk1 The enzymes of the hexokinase family catalyze the intracellular trapping and the initiation of metabolism of glucose, fructose, and mannose. In addition to their role in glycolysis, an increasing number of yeast, plant, and mammalian hexokinases have been found to represent multifunctional proteins that are implicated in glucose sensing and signaling (1)(2)(3)(4), whereas their glycolytic sugar substrate plays a dual role as a carbon source and hormone-like regulator (4,5). The molecular basis underlying the involvement of hexokinases in the transcriptional control of glucose metabolism and in glucose homeostasis is their ability to interact with mitochondria and to reversibly translocate to nuclei (3, 6 -9).…”

A network biology approach to aging in yeast

“…In a glucose-rich environment, the transcription factor (TF) Mig1 represses alternative carbon source metabolism and gluconeogenesis gene expression, including enzyme SUC2 and TF CAT8 (7,9,21). Hxk2, the predominant glucose kinase in the first step of glycolysis, shows glucose-dependent nuclear localization and associates with DNA-binding factors Mig1 and Mediator subunit Med8 at the promoter of SUC2 to repress its expression (24,25). Glucose exhaustion activates SNF1, which translocates from the cytoplasm to the nucleus and deactivates Mig1 by phosphorylation.…”

“…Glucose exhaustion activates SNF1, which translocates from the cytoplasm to the nucleus and deactivates Mig1 by phosphorylation. This triggers the translocation of Mig1 and Hxk2 to the cytoplasm, resulting in increased expression of SUC2, as well as CAT8, TF SIP4, and their downstream target FBP1 (7,25). Expression changes in response to calorie restriction (Fig.…”