title: Buried polar residues in coiled-coil interfaces.
abstract: Coiled coils, estimated to constitute 3-5% of the encoded residues in most genomes, are characterized by a heptad repeat, (abcdefg)(n), where the buried a and d positions form the interface between multiple alpha-helices. Although generally hydrophobic, a substantial fraction ( approximately 20%) of these a- and d-position residues are polar or charged. We constructed variants of the well-characterized coiled coil GCN4-p1 with a single polar residue (Asn, Gln, Ser, or Thr) at either an a or a d position. The stability and oligomeric specificity of each variant were measured, and crystal structures of coiled-coil trimers with threonine or serine at either an a or a d position were determined. The structures show how single polar residues in the interface affect not only local packing, but also overall coiled-coil geometry as seen by changes in the Crick supercoil parameters and core cavity volumes.
authors.affiliation: Howard Hughes Medical Institute, Whitehead Institute for Biomedical Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Akey
authors.forename: V N
authors.initials: VN
authors.lastname: Malashkevich
authors.forename: P S
authors.initials: PS
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000596:Amino Acids / Q000737:chemistry* / Q000235:genetics; D002942:Circular Dichroism; D003460:Crystallization; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics; D006358:Hot Temperature; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000235:genetics; D011494:Protein Kinases / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D012694:Serine / Q000235:genetics; D012996:Solutions; D013912:Threonine / Q000235:genetics; D014461:Ultracentrifugation
chemical_list: D000596:Amino Acids; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; D012996:Solutions; D013912:Threonine; D012694:Serine; D011494:Protein Kinases