Genes encoding l-arabinose transporters in Kluyveromyces marxianus and Pichia guilliermondii were identified by functional complementation of Saccharomyces cerevisiae whose growth on l-arabinose was dependent on a functioning l-arabinose transporter, or by screening a differential display library, respectively. These transporters also transport d-xylose and were designated KmAXT1 (arabinose-xylose transporter) and PgAXT1, respectively. Transport assays using l-arabinose showed that KmAxt1p has Km 263mm and Vmax 57nm/mg/min, and PgAxt1p has Km 0.13mm and Vmax 18nm/mg/min. Glucose, galactose and xylose significantly inhibit l-arabinose transport by both transporters. Transport assays using d-xylose showed that KmAxt1p has Km 27mm and Vmax 3.8nm/mg/min, and PgAxt1p has Km 65mm and Vmax 8.7nm/mg/min. Neither transporter is capable of recovering growth on glucose or galactose in a S. cerevisiae strain deleted for hexose and galactose transporters. Transport kinetics of S. cerevisiae Gal2p showed Km 371mm and Vmax 341nm/mg/min for l-arabinose, and Km 25mm and Vmax 76nm/mg/min for galactose. Due to the ability of Gal2p and these two newly characterized transporters to transport both l-arabinose and d-xylose, one scenario for the complete usage of biomass-derived pentose sugars would require only the low-affinity, high-throughput transporter Gal2p and one additional high-affinity general pentose transporter, rather than dedicated d-xylose or l-arabinose transporters. Additionally, alignment of these transporters with other characterized pentose transporters provides potential targets for substrate recognition engineering.
Knoshaug, E. P., Vidgren, V., Magalhães, F., Jarvis, E. E., Franden, M. A., Zhang, M., & Singh, A. (2015). Novel transporters from Kluyveromyces marxianus and Pichia guilliermondii expressed in Saccharomyces cerevisiae enable growth on L-arabinose and D-xylose. Yeast, 32(10), 615-628. https://doi.org/10.1002/yea.3084