A Member of the Sugar Transporter Family, Stl1p Is the Glycerol/H⁺Symporter inSaccharomyces cerevisiae

Abstract

Glycerol and other polyols are used as osmoprotectants by many organisms. Several yeasts and other fungi can take up glycerol by proton symport. To identify genes involved in active glycerol uptake in Saccharomyces cerevisiae we screened a deletion mutant collection comprising 321 genes encoding proteins with 6 or more predicted transmembrane domains for impaired growth on glycerol medium. Deletion of STL1, which encodes a member of the sugar transporter family, eliminates active glycerol transport. Stl1p is present in the plasma membrane in S. cerevisiae during conditions where glycerol symport is functional. Both the Stl1 protein and the active glycerol transport are subject to glucose-induced inactivation, following identical patterns. Furthermore, the Stl1 protein and the glycerol symporter activity are strongly but transiently induced when cells are subjected to osmotic shock. STL1 was heterologously expressed in Schizosaccharomyces pombe, a yeast that does not contain its own active glycerol transport system. In S. pombe, STL1 conferred the ability to take up glycerol against a concentration gradient in a proton motive force-dependent manner. We conclude that the glycerol proton symporter in S. cerevisiae is encoded by STL1. INTRODUCTIONGlycerol, a C 3 polyalcohol, is an important intermediate in energy metabolism in both prokaryotes and eukaryotes. It has long been used for therapeutic and industrial processes. Aspects of glycerol metabolism are also important in biotechnology, e.g., for bio-alcohol production yields or wine smoothness. Essential roles of glycerol in basic biochemical aspects have been extensively studied in several yeasts and fungi. These include biosynthesis of glycerophospholipid and triacylglycerol from glycerol 3-phosphate and dihydroxyacetone phosphate (Kohlwein et al., 1996;Mü llner and Daum, 2004), redox balance (Ansell et al., 1997;Valadi et al., 2004), osmoadaptation (reviewed by Hohmann, 2002, oxidative stress protection (Påhlman et al., 2001), and response to heat shock (Siderius et al., 2000). Responses to elevated temperatures and high osmolarity involve several signaling pathways including the protein kinase C pathway and the HOG pathway, which regulates intracellular levels of glycerol (Hohmann, 2002;Wojda et al., 2003).In cells ranging from mammals (Lang et al., 1998) to archea (Kempf and Bremer, 1998), osmolytes play an important role in the response to osmotic stress caused by low water availability in environments as diverse as poorly irrigated soils or high-sugar musts. In eukaryotic microorganisms like algae or yeasts, polyols, primarily glycerol, act as osmolytes (reviewed by Brown, 1977 andWang et al., 2001). Their production, consumption and retention are consequently tightly regulated and dynamic processes (reviewed by Hohmann, 2002). Magnaporthe grisea (rice blast) a phytopathogenic fungus with a strong impact on world economy, accumulates glycerol, which allows the penetration of the appressorium into the plant host cell (Thines et al., 2000). Glycerol has also...

Initiation of the transcriptional response to hyperosmotic shock correlates with the potential for volume recovery

“…We consider that gpd1D gpd2D cells might import glycerol faster than wild-type cells expressing rAQP9. Possibly, the gpd1D gpd2D mutant expresses an intrinsic glycerol uptake system similar to Stl1, which mediates this enhanced uptake [18]. This in turn results in a relatively fast volume recovery and a lower Hog1 nuclear accumulation amplitude and shorter period.…”

Long-term model predictive control of gene expression at the population and single-cell levels

“…Several genes are up-regulated in response to a hyperosmotic stress. These genes include the nonessential gene STL1, which codes for a glycerol proton symporter (24,25). We decided to use its native promoter (pSTL1) to drive the expression of yECitrine, a fluorescent reporter.…”

Osmoregulation in Saccharomyces cerevisiae via mechanisms other than the high-osmolarity glycerol pathway

“…Subsequently, Oliveira & Lucas, 2004 determined that while GUP1 and GUP2 are expressed constitutively, transient changes in their expression levels in response to osmotic stress before attaining equilibrium could not be ruled out. Ferreira et al (2005), on the other hand, determined that active glycerol uptake was not attributable not either Gup1p or Gup2p but to the glycerol/H + symporter Stl1p (sugar transporter like). Recent studies have confirmed that the apparent osmosensitivity of gup1D mutants is due to the involvement of Gup1p in glycosylphophotidyl inositol lipid membrane remodelling, rather than in glycerol uptake (Yoko-o et al, 2013).…”