title: Novel peptide foldameric motifs: a step forward in our understanding of the fully-extended conformation/3(10)-helix coexistence.
abstract: The fully-extended, multiple C(5), conformation or 2.0(5) helix is a very appealing peptide secondary structure, in particular for its potential use as a molecular spacer, as it is characterized by the longest elevation (as high as 3.62 Å) between the α-carbon atoms of two consecutive α-amino acids. Despite this intriguing property, however, it is only poorly investigated and understood. Here, using a complete series of C(α,α)-diethylglycine (Deg) homo-oligopeptide esters to the pentamer level, we exploited the properties of a fluorophore and a quencher, synthetically positioned at the N- and C-termini of the main chain, respectively, to check the applicability of the fully-extended conformation as a rigid molecular spacer. The fluorescence study was complemented by FT-IR absorption and NMR conformational investigations. The X-ray diffraction structures of selected compounds are also reported. Unfortunately, we find that, even in a solvent of low polarity, such as chloroform, in this peptide series an equilibrium does take place between the fragile fully-extended conformation and the 3(10)-helical structure, the latter becoming more and more stable as the main chain is elongated. Since the Deg homo-peptide esters lacking any terminal aromatic group, previously investigated, are known to adopt a stable fully-extended conformation in chloroform solution, we tend to attribute the 3D-structure instability observed in this work to the presence of multiple aromatic rings in their blocking groups.
authors.affiliation: ICB, Padova Unit, CNR, Department of Chemistry, University of Padova, 35131 Padova, Italy. fernando.formaggio@unipd.it
authors.forename: Fernando
authors.initials: F
authors.lastname: Formaggio
authors.forename: Marco
authors.initials: M
authors.lastname: Crisma
authors.forename: Gema
authors.initials: G
authors.lastname: Ballano
authors.forename: Cristina
authors.initials: C
authors.lastname: Peggion
authors.forename: Mariano
authors.initials: M
authors.lastname: Venanzi
authors.forename: Claudio
authors.initials: C
authors.lastname: Toniolo
mesh_terms: D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: D010455:Peptides