title: Model study using designed selenopeptides on the importance of the catalytic triad for the antioxidative functions of glutathione peroxidase.
abstract: Although the catalytic triad of glutathione peroxidase (GPx) has been well recognized, there was little evidence for the relevance of the interactions among the triad amino acid residues, i.e., selenocysteine (U), glutamine (Q), and tryptophan (W), to the GPx antioxidative functions. Using a designed selenopeptide having an amino acid sequence of GQAUAWG, we demonstrate here that U, Q, and W present at the active site can interact with each other to exert the enzymatic activity. The amino acid sequence was chosen on the basis of the Monte Carlo molecular simulation for various selenopeptides in polarizable continuous water using the SAAP force field (SAAP-MC). Measurement of the GPx-like activity for the selenopeptide obtained by solid-phase peptide synthesis revealed that the antioxidant activity is cooperatively enhanced by the presence of Q and W proximate to U, although the activity was low compared to selenocystine (U2). The effect of Q on the activity was more important than that of W. In addition, the fluorescence spectrometry suggested a close contact between U and W. These experimental observations were supported by SAAP-MC simulation as well as by ab initio calculation. The latter further suggested that the interaction mode among the triad changes depending on the intermediate states.
authors.affiliation: Department of Chemistry, School of Science, Tokai University , Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Takei
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Urabe
authors.forename: Yuya
authors.initials: Y
authors.lastname: Asahina
authors.forename: Hironobu
authors.initials: H
authors.lastname: Hojo
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nomura
authors.forename: Kenichi
authors.initials: K
authors.lastname: Dedachi
authors.forename: Kenta
authors.initials: K
authors.lastname: Arai
authors.forename: Michio
authors.initials: M
authors.lastname: Iwaoka
mesh_terms: D000595:Amino Acid Sequence; D000975:Antioxidants / Q000737:chemistry* / Q000378:metabolism; D055162:Biocatalysis; D020134:Catalytic Domain; D005973:Glutamine / Q000737:chemistry; D005979:Glutathione Peroxidase / Q000737:chemistry* / Q000378:metabolism; D009010:Monte Carlo Method; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017279:Selenocysteine / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry
chemical_list: D000975:Antioxidants; D010455:Peptides; D017279:Selenocysteine; D005973:Glutamine; D014364:Tryptophan; D005979:Glutathione Peroxidase