Display Settings:

Format

Send to:

Choose Destination
Biochemistry. 2013 Jun 25;52(25):4296-307. doi: 10.1021/bi4004638. Epub 2013 Jun 17.

Structural and functional implications of the yeast high-affinity tryptophan permease Tat2.

Author information

  • 1Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara, Japan.

Abstract

Tryptophan is hydrophobic, bulky, and the rarest amino acid found in nutrients. Accordingly, the import machinery can be specialized evolutionarily. Our previous study in Saccharomyces cerevisiae demonstrated that tryptophan import by the high-affinity tryptophan permease Tat2 is accompanied by a large volume increase during substrate import. Nevertheless, the mechanisms by which the permease mediates tryptophan recognition and permeation remain to be elucidated. Here we determined amino acid residues essential for Tat2-mediated tryptophan import. By means of random mutagenesis in combination with site-directed mutagenesis based on crystallographic studies of the Escherichia coli arginine/agmatine antiporter AdiC, we identified 15 amino acid residues in the Tat2 transmembrane domains (TMDs) 1, -3, -5, -8, and -10, which are responsible for tryptophan uptake. T98, Y167, and E286 were assumed to form the central cavity in Tat2. G97/T98 and E286 were located within the putative α-helix break in TMD1 and TMD6, respectively, which are highly conserved among yeast amino acid permeases and bacterial solute transporters. Given the conformational change in AdiC upon substrate binding, G97/T98 and E286 of Tat2 were assumed to mediate a structural shift from an outward-open to a tryptophan-bound-occluded structure upon tryptophan binding, and T320, V322, and F324 became stabilized in TMD7. Such dynamic structural changes may account for the large volume increase associated with tryptophan import occurring concomitantly with a movement of water molecules from the tryptophan binding site. We also propose the working hypothesis that E286 mediates the proton influx that is coupled to tryptophan import.

PMID:
23768406
[PubMed - indexed for MEDLINE]
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Icon for American Chemical Society
    Loading ...
    Write to the Help Desk