University of Groningen The Amino-Terminal Tail of Hxt11 Confers Membrane Stability to the Hxt2 Sugar Transporter and Improves Xylose Fermentation in the Presence of Acetic Acid

Hxt2 is a glucose repressed, high affinity glucose transporter of the yeast Saccharomyces cerevisiae and is subjected to high glucose induced degradation. Hxt11 is a sugar transporter that is stably expressed at the membrane irrespective the sugar concentration. To transfer this property to Hxt2, the N-terminal tail of Hxt2 was replaced by the corresponding region of Hxt11 yielding a chimeric Hxt11/2 transporter. This resulted in the stable expression of Hxt2 at the membrane and improved the growth on 8% D-glucose and 4% D-xylose. Mutation of N361 of Hxt11/2 into threonine reversed the specificity for D-xylose over D-glucose with high D-xylose transport rates. This mutant supported efficient sugar fermentation of both D-glucose and D-xylose at industrially relevant sugar concentrations even in the presence of the inhibitor acetic acid which is normally present in lignocellulosic hydrolysates. Biotechnol. Bioeng. 2017;114: 1937–1945. 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.