Poster Presentation 2-29

The Role of Phe⁴³¹ of Saccharomyces cerevisiae Hxt 4 Transporter in Transporting Glucose and Xylose

Miroslav Sedlak, Christopher Y. Chen and Nancy W. Y. Ho*

Laboratory of Renewable Resources Engineering (LORRE)

Purdue University, LORRE

500 Central Dr.

West Lafayette, IN, 47906

Phone/fax: (765)494-7046

E-mail: nwyho@ecn.purdue.edu

The naturally occurring Saccharomyces yeasts, particularly those capable of effectively fermenting glucose to ethanol, are unable to metabolize xylose aerobically or anaerobically. We succeeded in developing genetically engineered yeasts that effectively utilize xylose aerobically for growth as well as effectively co-ferment glucose and xylose to ethanol. However, our genetically engineered yeasts still utilize glucose much faster than xylose. One reason is that the Saccharomyces yeasts do not contain specific transporters for xylose but instead rely on glucose transporters to transport xylose. Unfortunately, the glucose transporters greatly favor glucose over xylose. Saccharomyces yeasts have at least 7 major glucose transporters (Hxt1-7) with varying affinities for glucose.  We studied the affinity of each yeast Hxt transporters for xylose and found that Hxt 4 is one of the transporters with moderate affinity to glucose and xylose. We believe that converting such an Hxt transporter to solely transport xylose could lead to the development of yeast that ferments xylose more efficiently. It was reported that Phe⁴³¹ is crucial for yeast Hxt 2 to transport glucose.  In this presentation, we report our recent finding on the role of Phe⁴³¹ in Hxt 4 for transporting glucose and xylose.