title: An accessible hydrophobic surface is a key element of the molecular chaperone action of Atp11p.
abstract: Atp11p is a soluble protein of mitochondria that binds unassembled beta subunits of the F(1)-ATPase and prevents them from aggregating in the matrix. In this report, we show that Atp11p protects the insulin B chain from aggregating in vitro and therefore acts as a molecular chaperone. The chaperone action of Atp11p is mediated by hydrophobic interactions. An accessible hydrophobic surface in Atp11p was identified with the environment-sensitive fluorescent probe 1,1'-bis(4-anilino-5-napththalenesulfonic acid (bis-ANS). The spectral changes of bis-ANS in the presence of Atp11p indicate that the probe binds to a nonpolar region of the protein. Furthermore, the dye quenches the fluorescence of Atp11p tryptophan residues in a concentration-dependent manner. Although up to three molecules of bis-ANS can bind cooperatively to Atp11p, the binding of only one dye molecule is sufficient to virtually eliminate the chaperone activity of the protein.
authors.affiliation: Department of Surgery, Wayne State University School of Medicine, 1225 Ellman Bldg., 421 E. Canfield Ave., Detroit, MI 48201, USA.
authors.forename: D
authors.initials: D
authors.lastname: Sheluho
authors.forename: S H
authors.initials: SH
authors.lastname: Ackerman
mesh_terms: D000817:Anilino Naphthalenesulfonates / Q000494:pharmacology; D001665:Binding Sites; D004735:Energy Transfer; D005456:Fluorescent Dyes; D005656:Fungal Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D025261:Mitochondrial Proton-Translocating ATPases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D000817:Anilino Naphthalenesulfonates; D005456:Fluorescent Dyes; D005656:Fungal Proteins; D007328:Insulin; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C035763:5,5'-bis(8-(phenylamino)-1-naphthalenesulfonate); C098664:ATP11 protein, S cerevisiae; D025261:Mitochondrial Proton-Translocating ATPases