title: Sequence determinants of a conformational switch in a protein structure.
abstract: The Arc repressor of bacteriophage P22 is a dimeric member of the ribbon-helix-helix family of transcription factors. Residues 9-14 of each wild-type Arc subunit pair to form two antiparallel beta-strands and have the alternating pattern of polar and nonpolar residues expected for a beta-ribbon with one solvent-exposed face and one face that forms part of the hydrophobic core. Simultaneously switching Asn-11 to Leu and Leu-12 to Asn changes the local binary sequence pattern to that of an amphipathic helix. Previous studies have shown that this double mutation results in replacement of the wild-type beta-ribbon by two right-handed 3(10)-helices. Moreover, an Arc variant bearing just the Asn-11 --> Leu mutation has an ambiguous binary pattern and can form either the ribbon or the helical structures, which interchange rapidly. Here, we study Arc mutants in which position 11 is occupied by Gly, Ala, Val, Ile, Leu, Met, Phe, or Tyr. These mutants adopt the wild-type beta-ribbon structure in a sequence context that stabilizes this fold, but they assume the alternative helical structure in a sequence background in which the wild-type fold is precluded by negative design. In an otherwise wild-type sequence background, the detailed chemical properties of the position 11 side chain dictate which of the two competing conformational folds is preferred.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Anderson
authors.forename: Matthew H J
authors.initials: MH
authors.lastname: Cordes
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
mesh_terms: D000595:Amino Acid Sequence; D017100:Bacteriophage P22 / Q000737:chemistry* / Q000235:genetics; D002942:Circular Dichroism; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D012097:Repressor Proteins