Trehalose‐6‐phosphate, a new regulator of yeast glycolysis that inhibits hexokinases

Abstract

Tre~lo~6-phosphate (P) ~mpetitively inhibited the hexokinases from ~~cc~omyee~ cerevisiae. The strongest inhibition was observed upon hexokinase II, with a K, of 40 FM, while in the case of hexoklnase I the K, was 200 NM. Glucokinase was not inhibited by trehalose-6-P up to 5 mM. This inhibition appears to have physiological significance, since the intracellular levels of trehalose-6-P were about 0.2 mM. Hexokinases from other organisms were also inhibited, while glucokinases were unaffected. The hexokinase from the yeast, Yarrowia iipolytica, was particularly sensitive to the inhibition by trehalose-6-P: when assayed with 2 mM fructose an apparent K, of 5 PM was calculated. Two 5. cerevisiae mutants with abnormal levels of trehalose-6-P exhibited defects in glucose metabolism. It is concluded that trehalose-6-P plays an important role in the regulation of the first steps of yeast glycolysis, mainly through the inhibition of hexokinase II.Trehalose-6-phosphate; Hexokinase; Glycolysis; Yeast PRODUCTIONControl of the glycolytic flux in Succhurowryces cerevisicze has been considered to occur mainly at the level of phosphofructokinase and pyruvate kinase. Phosphofructokinase is regulated through activation by fructose-2,6-bisphosphate, phosphate (P) and AMP, and inhibition by ATP, while pyruvate kinase activity is modulated by its activation by fructose-l,(i-bisphosphate (for a review see [l]). However, since phosphof~~tokinase does not catalyze the first irreversible step in the utilization of glucose, its regulation is not sufficient to control the rate of glucose utilization, and thus some mechanism should exist to regulate the rate of glucose transport, phosphorylation, or both. Regulation of glucose transport by glucose-6-P was suggested by Sols [2], but experimental results obtained using mutants affected in phosphoglucose isomerase activity did not support this idea [3,4]. Besides, none of the yeast kinases that phosphorylate glucose are sensitive to glucose-6-P, in contrast with the mammalian hexokinase PI-The need for a regulation of the first steps of yeast glycolysis is illustrated by the pattern of ambulation of metabolites in certain yeast mutants upon addition of glucose [6-81. Yeast strains carrying the mutations fdpl [6] or cifl [7] do not grow on glucose, although the glycolytic enzymes are operative. These mutations turned out to be allelic [9], and strains bearing them become depleted of ATP upon addition of glucose and accumulate fructose-l ,6-bisphosphate up to 20 mM [6,7,10], suggesting that the rate of the first glycolytic steps exceeds the capacity of the glycolytic pathway. The sequence of the CIFZ gene [lo] encodes the small subunit of the trehalose-6-P synthase/trehalose-6-P phosphatase complex [ 11,123. A plausible explanation for the growth behaviour and the metabolic defects of cifl strains could be that either trehalose or trehalose-6-P play a role in the regulation of the yeast glycolytic flux. We show in this article that trehalose-6-P inhibits sugar phospho~lation.The stron~st inh...

Characterization and Regulation of the Trehalose Synthesis Pathway and Its Importance in the Pathogenicity of Cryptococcus neoformans

“…T6P is an intermediate in trehalose biosynthesis that has been shown to possess regulatory potential (5,26 (7,21,22,47,53,59) and give further insights into T6P. In C. albicans, the tps2 mutant flocculates during stationary growth, while in A. nidulans, the mutant produces nonviable germination of spores through a deficiency in chitin production.…”

“…Trehalose can also act as a membrane protectant during stressful conditions (14). On the other hand, some investigators have suggested that trehalose might also act as a reserve carbon source (23,31,36,51) and that trehalose-6-phosphate (T6P) can regulate hexokinase II and thus glycolytic flux in some fungi (5). Although its use as an energy source remains somewhat controversial, it has been definitively linked to sporulation in fungi (37).…”

Can yeast glycolysis be understood in terms of in vitro kinetics of the constituent enzymes? Testing biochemistry

“…Competitive inhibition by Tps1's metabolic product trehalose 6-phosphate may offer a mechanism [73]. In our model, as in all other published ones, no Tps1-mediated feedback mechanism was incorporated, as the feedback has not been characterized kinetically (see main text for the consequences).…”

Structural analysis of the subunits of the trehalose‐6‐phosphate synthase/phosphatase complex in Saccharomyces cerevisiae and their function during heat shock

“…Several mutations described earlier as fdp1, cif1, byp1, and glc6 have been shown to be alleles of the same gene and to exert a wide range of pleiotropic phenotypes (reviewed in Thevelein and Hohmann, 1995). An important phenotype of all these mutants (except glc6), however, is that they are unable to grow on glucose, apparently because of an uncontrolled influx of glucose into the glycolytic pathway (Van Aelst et al, 1991;Hohmann et al, 1993;Blá zquez et al, 1993;Blá zquez and Gancedo, 1994). At least three different models for this unexpected role of Tps1 (also called Ggs1 in this context) in the control of glycolysis have been presented, as follows.…”