title: Copper(I) stabilization by cysteine/tryptophan motif in the extracellular domain of Ctr4.
abstract: Copper transporter Ctr4 of fission yeast has a quasi-palindromic sequence rich in cysteine and aromatic amino acid residues, CX4YWNWYX4C (where X represents any amino acid), in the N-terminal extracellular domain. A 24-mer peptide comprising this sequence is bound to Cu(I) through the cysteine thiolate coordination. Luminescence, UV absorption and resonance Raman spectra of the Cu(I)-peptide complex show that at least one of the two tryptophan side chains is located in close proximity to the thiolate-Cu(I) center and interacts with the Cu(I) ion via π-electrons of the indole ring. Although the thiolates and Cu(I) are oxidized to disulfide and Cu(II), respectively, only very slowly in air-saturated solutions, replacements of the tryptophan residues to phenylalanine significantly accelerate the oxidation reactions. The results obtained indicate that the interaction between Cu(I) and tryptophan via π-electrons plays a significant role in protecting the thiolate-Cu(I) center against the oxidation. The cysteine- and tryptophan-rich quasi-palindromic sequence may be a metal binding motif that stabilizes Cu(I) in the oxidizing extracellular environment.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Okada
authors.affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan. Electronic address: tmiura@m.tohoku.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Miura
mesh_terms: D020816:Amino Acid Motifs; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D000072417:Protein Domains; D055550:Protein Stability; D000080083:SLC31 Proteins; D012568:Schizosaccharomyces / Q000737:chemistry* / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry* / Q000378:metabolism; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; C509405:Ctr4 protein, S pombe; D000080083:SLC31 Proteins; D029702:Schizosaccharomyces pombe Proteins; D003300:Copper; D014364:Tryptophan; D003545:Cysteine
keywords: Cation–π interaction; Ctr4 copper transporter; Cysteine; Metal coordination; Raman spectroscopy; Tryptophan