Rat brain hexokinase: Location of the allosteric regulatory site in a structural domain at the N-terminus of the enzyme

White, Tracy K.; Wilson, John E.

doi:10.1016/0003-9861(87)90506-6

Cited by 57 publications

(20 citation statements)

References 25 publications

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“…The C-terminal half of HKI is catalytically active, whereas the N-terminal half is inactive (3)(4)(5). Whereas G6P binds to both halves of HKI (3,5), the G6P regulatory site of HKI is thought to be in the N-half of the intact enzyme, and the C-half binding site is latent (1,6). In contrast, we have shown that both the N-and C-terminal halves of human and rat HKII (N-HKII and C-HKII, respectively) have catalytic activity and that each is inhibited by G6P (7).…”

mentioning

confidence: 73%

Functional Interaction between the N- and C-terminal Halves of Human Hexokinase II

Ardehali

Printz

Whitesell

et al. 1999

Journal of Biological Chemistry

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Mammalian hexokinases (HKs) I-III are composed of two highly homologous ϳ50-kDa halves. Studies of HKI indicate that the C-terminal half of the molecule is active and is sensitive to inhibition by glucose 6-phosphate (G6P), whereas the N-terminal half binds G6P but is devoid of catalytic activity. In contrast, both the N-and C-terminal halves of HKII (N-HKII and C-HKII, respectively) are catalytically active, and when expressed as discrete proteins both are inhibited by G6P. However, C-HKII has a significantly higher K i for G6P (K iG6P ) than N-HKII. We here address the question of whether the high K iG6P of the C-terminal half (C-half) of HKII is decreased by interaction with the N-terminal half (N-half) in the context of the intact enzyme. A chimeric protein consisting of the N-half of HKI and the C-half of HKII was prepared. Because the N-half of HKI is unable to phosphorylate glucose, the catalytic activity of this chimeric enzyme depends entirely on the C-HKII component. The K iG6P of this chimeric enzyme is similar to that of HKI and is significantly lower than that of C-HKII. When a conserved amino acid (Asp 209 ) required for glucose binding is mutated in the N-half of this chimeric protein, a significantly higher K iG6P (similar to that of C-HKII) is observed. However, mutation of a second conserved amino acid (Ser 155 ), also involved in catalysis but not required for glucose binding, does not increase the K iG6P of the chimeric enzyme. This resembles the behavior of HKII, in which a D209A mutation results in an increase in the K iG6P of the enzyme, whereas a S155A mutation does not. These results suggest an interaction in which glucose binding by the N-half causes the activity of the C-half to be regulated by significantly lower concentrations of G6P.Hexokinases (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1; HK) 1 catalyze the phosphorylation of glucose to glucose 6-phosphate (G6P). Type I, II, and III isozymes of mammalian HKs are ϳ100 kDa in size and are inhibited by the reaction product, G6P. Type IV HK (also known as glucokinase) is similar to yeast HK in that it has a relative mass of ϳ50 kDa and is insensitive to inhibition by physiologic concentrations of G6P. The deduced amino acid sequences of HKI-III reveal internal similarities between their N-and C-terminal halves and between each of these and yeast HK and glucokinase (1). This observation supports the hypothesis that the 100-kDa mammalian HKs evolved from the duplication and fusion of an ancestral 50-kDa HK (1, 2). The N-and C-terminal halves of HKI show a marked functional difference despite the similarity of their amino acid sequences. The C-terminal half of HKI is catalytically active, whereas the N-terminal half is inactive (3-5). Whereas G6P binds to both halves of HKI (3, 5), the G6P regulatory site of HKI is thought to be in the N-half of the intact enzyme, and the C-half binding site is latent (1, 6). In contrast, we have shown that both the N-and C-terminal halves of human and rat HKII (N-HKII and C-HKII, respectively) have cat...

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mentioning

confidence: 73%

Functional Interaction between the N- and C-terminal Halves of Human Hexokinase II

Ardehali

Printz

Whitesell

et al. 1999

Journal of Biological Chemistry

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“…Several studies have demonstrated a functional interaction between the two halves of HKI and HKII. G6P regulation of the C-terminal half of HKI is believed to be through its binding to the N-terminal half (53,55), and glucose binding by the N-terminal half of HKII causes the activity of the C-terminal half to be regulated by significantly lower concentrations of G6P (4). Thus, the physical and functional interaction between the two halves of HKI and HKII may also influence the antiapoptotic effects of these enzymes.…”

Section: Discussionmentioning

confidence: 99%

Glucose Phosphorylation and Mitochondrial Binding Are Required for the Protective Effects of Hexokinases I and II

Sun

Shukair

Naik

et al. 2008

Molecular and Cellular Biology

220

224

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“…The corresponding physical assignment of specific regulatory functions to structural regions of individual isoforms is more controversial and has been reviewed elsewhere (Wilson, 1997a;Cardenas et al, 1998). Glucose-6-phosphate regulatory function, originally predicted to reside at a single site in the amino-terminus of intact HKI (White and Wilson, 1987), has been shown to represent an intrinsic feature of the carboxylterminal half of this isoform (White and Wilson, 1989;Arora et al, 1993). To reconcile these findings, it has been suggested that regulatory domains identified in individual hemidomains may reside in a latent or masked form in the intact enzyme (Wilson, 1997a).…”

Section: Mammalian Cells Express Multiple Hexokinase Isoformsmentioning

confidence: 99%

Mitochondrial hexokinases, novel mediators of the antiapoptotic effects of growth factors and Akt

2006

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Cell survival has been closely linked to both trophic growth factor signaling and cellular metabolism. Such couplings have obvious physiologic and pathophysiologic implications, but their underlying molecular bases remain incompletely defined. As a common mediator of both the metabolic and anti-apoptotic effects of growth factors, the serine/threonine kinase Akt -also known as protein kinase B or PKB -is capable of regulating and coordinating these inter-related processes. The glucose dependence of the antiapoptotic effects of growth factors and Akt plus a strong correlation between Akt-regulated mitochondrial hexokinase association and apoptotic susceptibility suggest a major role for hexokinases in these effects. Mitochondrial hexokinases catalyse the first obligatory step of glucose metabolism and directly couple extramitochondrial glycolysis to intramitochondrial oxidative phosphorylation, and are thus well suited to play this role. The ability of Akt to regulate energy metabolism appears to have evolutionarily preceded the capacity to control cell survival. This suggests that Akt-dependent metabolic regulatory functions may have given rise to glucose-dependent antiapoptotic effects that evolved as an adaptive sensing system involving hexokinases and serve to ensure mitochondrial homeostasis, thereby coupling metabolism to cell survival. We hypothesize that the enlistment of Akt and hexokinase in the control of mammalian cell apoptosis evolved as a response to the recruitment of mitochondria to the apoptotic cascade. The central importance of mitochondrial hexokinases in cell survival also suggests that they may represent viable therapeutic targets in cancer.

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Rat brain hexokinase: Location of the allosteric regulatory site in a structural domain at the N-terminus of the enzyme

Cited by 57 publications

References 25 publications

Functional Interaction between the N- and C-terminal Halves of Human Hexokinase II

Functional Interaction between the N- and C-terminal Halves of Human Hexokinase II

Glucose Phosphorylation and Mitochondrial Binding Are Required for the Protective Effects of Hexokinases I and II

Mitochondrial hexokinases, novel mediators of the antiapoptotic effects of growth factors and Akt

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