title: Experimental investigation of initial steps of helix propagation in model peptides.
abstract: It is not certain whether the helix propagation parameters s(n)() (i.e., the equilibrium constants between (n - 1)- and n-residue long alpha-helices) determined from numerous studies of rather long model peptides are applicable for description of the initial steps of the helix formation during the protein folding process. From fluorescence, NMR, and calorimetric studies of a series of model peptides, containing the La(3+)-binding sequence nucleating the helix (Siedlecka, M., Goch, G., Ejchart, A., Sticht, H., and Bierzynski, A. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 903-908), we have determined, at 25 degrees C, the average values of the enthalpy DeltaH(n)() and of the helix growth parameters s(n)() describing the first four steps of helix propagation in polyalanine. The absolute values of the C-cap parameters, describing the contribution of the C-terminal residues to the helix free energy, have also been estimated for alanine (1.2 +/- 0.5) and NH(2) group (1.6 +/- 0.7). The initial four steps of the helix growth in polyalanine can be described by a common propagation parameter s = 1.54 +/- 0.04. The enthalpy DeltaH(n)() is also constant and equals -980 +/- 100 cal mol(-)(1).
authors.affiliation: Institute of Biochemistry and Biophysics, Polish Academy of Sciences, ul. Pawińskiego 5A, 02-106 Warsaw, Poland.
authors.forename: Grazyna
authors.initials: G
authors.lastname: Goch
authors.forename: Maciej
authors.initials: M
authors.lastname: Maciejczyk
authors.forename: Marta
authors.initials: M
authors.lastname: Oleszczuk
authors.forename: Damian
authors.initials: D
authors.lastname: Stachowiak
authors.forename: Joanna
authors.initials: J
authors.lastname: Malicka
authors.forename: Andrzej
authors.initials: A
authors.lastname: Bierzyński
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000737:chemistry* / Q000235:genetics; D010455:Peptides / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D009842:Oligopeptides; D010455:Peptides; C019529:polyalanine