title: Importance of potential interhelical salt-bridges involving interior residues for coiled-coil stability and quaternary structure.
abstract: Coiled coils are formed by two or more alpha-helices that align in a parallel or an antiparallel relative orientation. Polar interactions involving residues at the interior a and d positions are important for determining the quaternary structure of coiled coils. In the model heterodimeric coiled-coil Acid-a1-Base-a1, a buried a-d' Asn-Asn interaction is sufficient to specify both a dimeric structure and an antiparallel relative helix orientation. Although the equivalent a-a' interaction is found in parallel coiled coils, there is no example of an a-d' Asn-Asn interaction in structurally characterized, naturally occurring antiparallel coiled coils. Instead, interior charged residues form interhelical salt-bridges with residues at the adjacent e or g positions. Using a model coiled-coil heterodimer, we have explored the role of a potential interhelical interaction between an Arg at an interior d position and a Glu at the adjacent g' position. Our results demonstrate that this potentially attractive interhelical Coulombic interaction has little or no influence on helix orientation. Instead, we show that burying a single Arg residue at an interior position is sufficient to specify a dimeric state at a significantly lower thermodynamic cost than burial of two interacting Asn residues.
authors.affiliation: Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, IN 47405-7102, USA.
authors.forename: Diana L
authors.initials: DL
authors.lastname: McClain
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Gurnon
authors.forename: Martha G
authors.initials: MG
authors.lastname: Oakley
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D019281:Dimerization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000737:chemistry* / Q000378:metabolism; D055672:Static Electricity; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D010455:Peptides; D013438:Sulfhydryl Compounds; D012965:Sodium Chloride