title: Cysteine labeling studies detect conformational changes in region 106-132 of the mitochondrial ADP/ATP carrier of Saccharomyces cerevisiae.
abstract: To know the structural and functional features of the cytosolic-facing first loop (LC1) including its surrounding region of the mitochondrial ADP/ATP carrier (AAC), we prepared 27 mutants, in which each amino acid residue between residues 106 and 132 of the yeast type 2 AAC (yAAC2) was replaced by a cysteine residue. For mutant preparation, we used a Cys-less AAC mutant, in which all four intrinsic cysteine residues were substituted with alanine residues, as a template [Hatanaka, T., Kihira, Y., Shinohara, Y., Majima, E., and Terada, H. (2001) Biochem. Biophys. Res. Commun. 286, 936-942]. From the labeling intensities of the membrane-impermeable SH-reagent eosin-5-maleimide (EMA), sequence Lys(108)-Phe(127) was suggested to constitute the LC1. The N-terminal half of this region (Lys(108)-Phe(115)) was suggested to change its location from the cytosol to a region close to the membrane on conversion from the c-state to the m-state in association with disruption or unwinding of its alpha-helical structure, whereas the C-terminal half region (Gly(116)-Phe(127)) was considered to extrude essentially into the cytosol, while keeping its alpha-helical structure. Hence, the conformation of m-state LC1 is greatly different from that of c-state LC1. Possibly the LC1 changes its location between the membranous region and the cytosol during ADP/ATP transport. Lys(108) in the LC1 of the yAAC2 was found to be associated with binding of the transport substrates, and its -NH(3)(+) moiety, to be of importance for the transport function. On the basis of these results, possible roles of the conformational changes of the LC1 in the transport activity are discussed.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of Tokushima, Shomachi-1, Tokushima 770-8505, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Kihira
authors.forename: Eiji
authors.initials: E
authors.lastname: Majima
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Shinohara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Terada
mesh_terms: D000818:Animals; D001692:Biological Transport; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D003545:Cysteine; D003600:Cytosol / Q000201:enzymology; D000226:Mitochondrial ADP, ATP Translocases / Q000737:chemistry*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D010446:Peptide Fragments; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D000226:Mitochondrial ADP, ATP Translocases; D003545:Cysteine