title: Retention of chimeric Tat2-Gap1 permease in the endoplasmic reticulum induces unfolded protein response in Saccharomyces cerevisiae.
abstract: In Saccharomyces cerevisiae, high-affinity tryptophan import is performed by subtle mechanisms involving tryptophan permease Tat2. We have shown that Tat2 requires 15 amino acid residues in the transmembrane domains (TMDs) for its import activity, whereas leucine permease Bap2 requires only seven corresponding residues for its leucine import. For this reason, the structure of Tat2 is elaborately designed to transport the hydrophobic and bulky tryptophan. Newly synthesized cell surface proteins first undergo endoplasmic reticulum (ER)-associated quality check before entering the secretory pathway. In this study, we used domain replacement with general amino acid permease Gap1 to show that Tat2 chimeric proteins were dysfunctional when TMD10 or TMD11 was replaced. These chimeras formed large 270-800-kDa protein complexes and were stably retained in the ER membrane without efficient degradation. In contrast, Tat2 chimeras of TMD9 or TMD12 retained some of their tryptophan import activity and underwent vacuolar degradation as observed with wild-type Tat2. Thus, ours results suggest that TMD10 and TMD11 are essential for the correct folding of Tat2, probably because of their interdomain interactions. Notably, overexpression of Tat2-Gap1 chimera of TMD10 activated the unfolded protein response (UPR) element-lacZ reporter, suggesting that ER retention of the protein aggregates induces the UPR.
authors.affiliation: Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara 252-5258, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Mochizuki
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma 630-0192, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kimata
authors.affiliation: Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara 252-5258, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Uemura
authors.affiliation: Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, Sagamihara 252-5258, Japan abef@chem.aoyama.ac.jp.
authors.forename: Fumiyoshi
authors.initials: F
authors.lastname: Abe
mesh_terms: D026905:Amino Acid Transport Systems / Q000235:genetics* / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D017510:Protein Folding; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D056811:Unfolded Protein Response / Q000235:genetics*
chemical_list: D026905:Amino Acid Transport Systems; C491145:GAP1 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C429825:TAT2 protein, S cerevisiae
keywords: ER retention; Saccharomyces cerevisiae; TMD chimeric protein; general amino acid permease Gap1; tryptophan permease Tat2; unfolded protein response