title: Effects of turn residues in directing the formation of the beta-sheet and in the stability of the beta-sheet.
abstract: The designed peptide (denoted 20-mer, sequence VFITS(D)PGKTYTEV(D)PGOKILQ) has been shown to form a three-strand antiparallel beta-sheet. It is generally believed that the (D)Pro-Gly segment has the propensity to adopt a type II' beta-turn, thereby promoting the formation of this beta-sheet. Here, we replaced (D)Pro-Gly with Asp-Gly, which should favor a type I' turn, to examine the influence of different type of turns on the stability of the beta-sheet. Contrary to our expectation, the mutant peptide, denoted P6D, forms a five-residue type I turn plus a beta-bulge between the first two strands due to a one amino-acid frameshift in the hydrogen bonding network and side-chain inversion of the first beta-strand. In contrast, the same kind of substitution at (D)Pro-14 in the double mutant, denoted P6DP14D, does not yield the same effect. These observations suggest that the SDGK sequence disfavors the type I' conformation while the VDGO sequence favors a type I' turn, and that the frameshift in the first strand provides a way for the peptide to accommodate a disfavored turn sequence by protruding a bulge in the formation of the beta-hairpin. Thus, different types of turns can affect the stability of a beta-structure.
authors.affiliation: Institute of Chemistry, Academia Sinica, Taipei, Taiwan, ROC.
authors.forename: P Y
authors.initials: PY
authors.lastname: Chen
authors.forename: C K
authors.initials: CK
authors.lastname: Lin
authors.forename: C T
authors.initials: CT
authors.lastname: Lee
authors.forename: H
authors.initials: H
authors.lastname: Jan
authors.forename: S I
authors.initials: SI
authors.lastname: Chan
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002942:Circular Dichroism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D010455:Peptides