title: Structural impact of proline mutations in the loop region of an ancestral membrane protein.
abstract: The sodium ion-translocating F0 F1 ATP synthase from the bacterium Ilyobacter tartaricus contains a highly stable rotor ring composed of 11 c subunits. The synthase subunit c-in effect an 89-residue peptide that folds into a helical hairpin consisting of two membrane-spanning helices and a cytoplasmic loop-was probed for the structural impact of a series of substitutions with the β-turn-inducing proline-glycine couplet scanning the hairpin loop (residues 44-51) of the I. tartaricus sequence. We found that a Pro residue in other than the wild type position 47 alters the gross secondary structure of subunit c from α-helical to β-sheet-like, as well as changing its oligomeric ring structure, and its stability toward heat and trichloroacetic acid treatment. Such a Pro-mediated structural switch in one of the first membrane proteins in life hints to a potential evolutionary connection between α-helical and β-sheet membrane proteins.
authors.affiliation: Program in Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, M5G 1X8, Ontario, Canada.|Department of Biochemistry, University of Toronto, Toronto, M5S 1A8, Ontario, Canada.
authors.forename: Vincent G
authors.initials: VG
authors.lastname: Nadeau
authors.affiliation: Program in Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, M5G 1X8, Ontario, Canada.|Department of Biochemistry, University of Toronto, Toronto, M5S 1A8, Ontario, Canada.
authors.forename: Charles M
authors.initials: CM
authors.lastname: Deber
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D009154:Mutation; D011392:Proline / Q000235:genetics*; D011487:Protein Conformation
chemical_list: D008565:Membrane Proteins; D011392:Proline
keywords: ATP synthase; Pro-Gly couplet; helical hairpin; loop; membrane protein evolution; membrane protein folding; subunit c; β-turn