Transport of hemicellulose monomers in the xylose-fermenting yeastCandida shehatae

Abstract

Summary. Cells of Candida shehatae repressed by growth in glucose-or D-xylose-medium produced a facilitated diffusion system that transported glucose ( K s + 2 m M , Vm,x--+2.3 mmoles g-1 h-l), D-xylose (Ks + 125 mM, Vmax + 22.5 mmoles g-1 h-1) and D-mannose, but neither D-galactose nor L-arabinose.Cells derepressed by starvation formed several sugar-proton symports. One proton symport accumulated 3-0-methylglucose about 400-fold and transported glucose (Ks+0.12 mM, V m a x + 3 . 2 mmoles g-1 h-1) and D-mannose, a second proton symport transported D-xylose (Ks+ 1.0 mM, Vmax 1.4 mmoles g-1 h-1) and D-galactose, while L-arabinose apparently used a third proton symport. The stoicheiometry was one proton for each molecule of glucose or D-xylose transported. Substrates of one sugar proton symport inhibited non-competitively the transport of substrates of the other symports.Starvation, while inducing the sugar-proton symports, silenced the facilitated diffusion system with respect to glucose transport but not with respect to the transport of D-xylose, facilitated diffusion functioning simultaneously with the D-xylose-proton symport.

Control of xylose consumption by xylose transport in recombinant Saccharomyces cerevisiae

“…However, it would be beneficial to express an active xylose transporter, which is capable of taking up xylose in the cell against a concentration gradient, for utilization of xylose below 1 g L −1 (6.7 mM). Such transporters are common among the natural xylose utilizing yeasts (Alcorn and Griffin, 1978;Does and Bisson, 1989;Kilian and van Uden, 1988;Kilian et al, 1993;Lucas and van Uden, 1986;Nobre et al, 1999;Weierstall et al, 1999). In addition, it would be desirable to express a transporter, which is specific for xylose and not inhibited by glucose.…”

Engineering of yeast hexose transporters to transport d -xylose without inhibition by d -glucose

“…Avoiding transport inhibition in a cofermentation of cellobiose and xylose showed no impediments but even synergistic effects for a parallel catabolism (25). Inhibition of transport has also been directly verified by uptake assays for single transporters (11,26), as well as for S. cerevisiae (9) and different xylose-using yeast species (e.g., Candida shehatae, which also shows a sequential consumption of glucose and xylose) (27)(28)(29)(30). All known xylose transporters that can functionally be expressed in S. cerevisiae are neither selective for xylose, nor do they have a higher affinity for xylose, leading to competitive inhibition by glucose (31)(32)(33).…”

Bioethanol a Microbial Biofuel Metabolite; New Insights of Yeasts Metabolic Engineering

“…In S. cerevisiae, the uptake of L-arabinose appears to be mediated by the GAL2 transporter, as the L-arabinose structurally is analogous to D-galactose [200]. In C. shehatae, a proton symport seems to mediate the L-arabinose uptake [201]. Besides, D-arabinitol dehydrogenase, which has a role in another pathway, links D-xylulose to D-ribulose metabolism [172,202].…”