| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2005: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2004: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
Hxt2 and Hxt1 are high-affinity and low-affinity facilitative glucose transporter paralogs of Saccharomyces cerevisiae, respectively, that differ at 75 amino acid positions in their 12 transmembrane segments (TMs). Comprehensive analysis of chimeras of these two proteins has previously revealed that TMs 1, 5, 7, and 8 of Hxt2 are required for high-affinity glucose transport activity and that leucine-201 in TM5 is the most important in this regard of the 20 amino acid residues in these regions that differ between Hxt2 and Hxt1. To evaluate the importance of the remaining residues, we systematically shuffled the amino acids at these positions and screened the resulting proteins for high-affinity and high-capacity glucose transport activity. In addition to leucine-201 (TM5), four residues of Hxt2 (leucine-59 and leucine-61 in TM1, asparagine-331 in TM7, and phenylalanine-366 in TM8) were found to be important for such activity. Furthermore, phenylalanine-198 (TM5), alanine-363 (TM8), and either valine-316 (TM7) or alanine-368 (TM8) were found to be supportive of maximal activity. Construction of a homology model suggested that asparagine-331 interacts directly with the substrate and that the other identified residues may contribute to maintenance of protein conformation.
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