Open AccessEvidence for a dynamic role for proline376 in the purine–cytosine permease of Saccharomyces cerevisiae
Author(s) -
Ferreira Thierry,
Napias Christian,
Chevallier Jean,
Brèthes Daniel
Publication year - 1999
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.1999.00454.x
Subject(s) - hypoxanthine , permease , cytosine , saccharomyces cerevisiae , guanine , purine , biochemistry , active transport , conformational change , purine metabolism , chemistry , stereochemistry , binding site , membrane transport , biology , yeast , transporter , membrane , dna , gene , enzyme , nucleotide
The purine–cytosine permease (PCP), a carrier located in the plasma membrane of Saccharomyces cerevisiae , mediates the active transport of purine (adenine, guanine and hypoxanthine) and cytosine into the cell. Previous studies [Ferreira, T, Brèthes, D., Pinson, B., Napias, C. & Chevallier, J. et al . (1997) J. Biol. Chem. 272, 9697–9702] suggest that the hydrophilic segment 371–377 (‐I‐A‐N‐N‐I‐P‐N‐) of the polypeptide chain may play a key role in the correct three‐dimensional structure of the active carrier. This paper describes the effects of mutations in this particular segment: a four‐residue deletion, Δ374–377, and two substitutions, P376G and P376R. The Δ374–377 PCP was expressed in tiny amounts and was totally inactive. When compared with the wild‐type, the P376G PCP showed slightly decreased amounts and was able to transport the bases with significantly increased affinity and decreased turnover. The P376R PCP was normally expressed and targeted to the plasma membrane; however, despite a normal number of base‐binding sites [1000–1200 pmol·(mg protein) −1 ], this mutated carrier was completely unable to transport any of its ligands. In addition, the K d (app) for hypoxanthine binding was completely independent of the pH (within the range 3.5–6.0), showing that the conformational change induced by ligand binding was no longer present. Our results show that the 374–377 segment is essential for the expression and activity of this carrier. They also show that the P376 residue is part of an unusual secondary structure, probably a β‐turn motif, which must play a crucial dynamic role in the translocation process.