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Eukaryotic Cell, April 2008, p. 735-746, Vol. 7, No. 4
1535-9778/08/$08.00+0     doi:10.1128/EC.00028-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Identification of Hexose Transporter-Like Sensor HXS1 and Functional Hexose Transporter HXT1 in the Methylotrophic Yeast Hansenula polymorpha{triangledown}

Olena G. Stasyk,1 Mykola M. Maidan,2,3 Oleh V. Stasyk,1 Patrick Van Dijck,2,3 Johan M. Thevelein,2,3 and Andriy A. Sibirny1,4*

Institute of Cell Biology, National Academy of Sciences of Ukraine, Drahomanov Street 14/16, Lviv 79005, Ukraine,1 Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven,2 VIB Department of Molecular Microbiology, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium,3 Rzeszów University, Department of Biotechnology and Microbiology, Cwiklinskiej 2, 35-601 Rzeszów, Poland4

Received 23 January 2008/ Accepted 17 February 2008

We identified in the methylotrophic yeast Hansenula polymorpha (syn. Pichia angusta) a novel hexose transporter homologue gene, HXS1 (hexose sensor), involved in transcriptional regulation in response to hexoses, and a regular hexose carrier gene, HXT1 (hexose transporter). The Hxs1 protein exhibits the highest degree of primary sequence similarity to the Saccharomyces cerevisiae transporter-like glucose sensors, Snf3 and Rgt2. When heterologously overexpressed in an S. cerevisiae hexose transporter-less mutant, Hxt1, but not Hxs1, restores growth on glucose or fructose, suggesting that Hxs1 is nonfunctional as a carrier. In its native host, HXS1 is expressed at moderately low level and is required for glucose induction of the H. polymorpha functional low-affinity glucose transporter Hxt1. Similarly to other yeast sensors, one conserved amino acid substitution in the Hxs1 sequence (R203K) converts the protein into a constitutively signaling form and the C-terminal region of Hxs1 is essential for its function in hexose sensing. Hxs1 is not required for glucose repression or catabolite inactivation that involves autophagic degradation of peroxisomes. However, HXS1 deficiency leads to significantly impaired transient transcriptional repression in response to fructose, probably due to the stronger defect in transport of this hexose in the hxs1{Delta} deletion strain. Our combined results suggest that in the Crabtree-negative yeast H. polymorpha, the single transporter-like sensor Hxs1 mediates signaling in the hexose induction pathway, whereas the rate of hexose uptake affects the strength of catabolite repression.

* Corresponding author. Mailing address: Institute of Cell Biology, National Academy of Sciences of Ukraine, Drahomanov St. 14/16, Lviv 79005, Ukraine. Phone: 38-032-2612163. Fax: 38-032-2612148. E-mail: sibirny{at}cellbiol.lviv.ua

{triangledown} Published ahead of print on 29 February 2008.

Eukaryotic Cell, April 2008, p. 735-746, Vol. 7, No. 4
1535-9778/08/$08.00+0     doi:10.1128/EC.00028-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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