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Glucose-induced cAMP signalling in yeast requires both a G-protein coupled receptor system for extracellular glucose detection and a separable hexose kinase-dependent sensing process.

Abstract：

:In Saccharomyces cerevisiae, glucose activation of cAMP synthesis requires both the presence of the G-protein-coupled receptor (GPCR) system, Gpr1-Gpa2, and uptake and phosphorylation of the sugar. In a hxt-null strain that lacks all physiologically important glucose carriers, glucose transport as well as glucose-induced cAMP signalling can be restored by constitutive expression of the galactose permease. Hence, the glucose transporters do not seem to have a regulatory function but are only required for glucose uptake. We established a system in which the GPCR-dependent glucose-sensing process is separated from the glucose phosphorylation process. It is based on the specific transport and hydrolysis of maltose providing intracellular glucose in the absence of glucose transport. Preaddition of a low concentration (0.7 mM) of maltose to derepressed hxt-null cells and subsequent addition of glucose restored the glucose-induced cAMP signalling, although there was no glucose uptake. Addition of a low concentration of maltose itself does not increase the cAMP level but enhances Glu6P and apparently fulfils the intracellular glucose phosphorylation requirement for activation of the cAMP pathway by extracellular glucose. This system enabled us to analyse the affinity and specificity of the GPCR system for fermentable sugars. Gpr1 displayed a very low affinity for glucose (apparent Ka = 75 mM) and responded specifically to extracellular alpha and beta D-glucose and sucrose, but not to fructose, mannose or any glucose analogues tested. The presence of the constitutively active Gpa2val132 allele in a wild-type strain bypassed the requirement for Gpr1 and increased the low cAMP signal induced by fructose and by low glucose up to the same intensity as the high glucose signal. Therefore, the low cAMP increases observed with fructose and low glucose in wild-type cells result only from the low sensitivity of the Gpr1-Gpa2 system and not from the intracellular sugar kinase-dependent process. In conclusion, we have shown that the two essential requirements for glucose-induced activation of cAMP synthesis can be fulfilled separately: an extracellular glucose detection process dependent on Gpr1 and an intracellular sugar-sensing process requiring the hexose kinases.

journal_name

Mol Microbiol

journal_title

Molecular microbiology

authors

Rolland F,De Winde JH,Lemaire K,Boles E,Thevelein JM,Winderickx J

doi

10.1046/j.1365-2958.2000.02125.x

subject

Has Abstract

pub_date

2000-10-01 00:00:00

pages

348-58

issue

eissn

0950-382X

issn

1365-2958

pii

mmi2125

journal_volume

pub_type

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Glucose-induced cAMP signalling in yeast requires both a G-protein coupled receptor system for extracellular glucose detection and a separable hexose kinase-dependent sensing process.