title: Flexibility of alpha-helices: results of a statistical analysis of database protein structures.
abstract: Alpha-helices stand out as common and relatively invariant secondary structural elements of proteins. However, alpha-helices are not rigid bodies and their deformations can be significant in protein function (e.g. coiled coils). To quantify the flexibility of alpha-helices we have performed a structural principal-component analysis of helices of different lengths from a representative set of protein folds in the Protein Data Bank. We find three dominant modes of flexibility: two degenerate bend modes and one twist mode. The data are consistent with independent Gaussian distributions for each mode. The mode eigenvalues, which measure flexibility, follow simple scaling forms as a function of helix length. The dominant bend and twist modes and their harmonics are reproduced by a simple spring model, which incorporates hydrogen-bonding and excluded volume. As an application, we examine the amount of bend and twist in helices making up all coiled-coil proteins in SCOP. Incorporation of alpha-helix flexibility into structure refinement and design is discussed.
authors.affiliation: NEC Research Institute, 4 Independence Way, Princeton, NJ 08540, USA.
authors.forename: Eldon G
authors.initials: EG
authors.lastname: Emberly
authors.forename: Ranjan
authors.initials: R
authors.lastname: Mukhopadhyay
authors.forename: Ned S
authors.initials: NS
authors.lastname: Wingreen
authors.forename: Chao
authors.initials: C
authors.lastname: Tang
mesh_terms: D030562:Databases, Protein; D008956:Models, Chemical; D008958:Models, Molecular; D018583:Pliability; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*
chemical_list: D011506:Proteins