Studies of poly-beta-benzyl-l-aspartate helix. II. The circular dichroism and optical rotatory dispersion of copolymers of beta-p-methyl, chloro, or cynabenzyl-l-aspartate with beta-benzyl-l-aspartate

Secondary Structures in Synthetic Poly(Amino Acids): Homo- and Copolymers of Poly(Aib), Poly(Glu), and Poly(Asp)

The secondary structure of poly(amino acids) is an excellent tool for controlling and understanding the functionality and properties of proteins. In this perspective article the secondary structures of the homopolymers of oligo- and poly-glutamic acid (Glu), aspartic acid (Asp), and α-aminoisobutyric acid (Aib) are discussed. Information on external and internal factors, such as the nature of side groups, interactions with solvents and interactions between chains is reviewed. A special focus is directed on the folding in hybrid-polymers consisting of oligo(amino acids) and synthetic polymers. Being part of the SFB TRR 102 "Polymers under multiple constraints: restricted and controlled molecular order and mobility" this overview is embedded into the cross section of protein fibrillation and supramolecular polymers. As polymer- and amino acid folding is an important step for the utilization and design of future biomolecules these principles guide to a deeper understanding of amyloid fibrillation.

Reversible helix sense inversion in surface-grafted poly(beta-phenethyl-L-aspartate) films

The reversible manipulation of the helix screw sense in surface-grafted poly(beta-phenethyl-L-aspartate) (PPELA) films by means of external stimuli was investigated. Ringopening polymerization of beta-phenethyl-L-aspartate N-carboxyanhydride initiated from primary amino-functionalized silicon and quartz substrates results in surface-grafted PPELA films in which the end-grafted polypeptide chains have a right-handed alpha-helical conformation. Upon annealing of the film at 150 degrees C for 30 min, a helix screw sense inversion takes place and the grafted chains adopt a left-handed pi-helical conformation. In the solid state, this left-handed pi-helical form is completely stable and cannot be changed by reheating and/or cooling. Upon immersion of the annealed grafted film in chloroform or other helicogenic solvents, the grafted polypeptide chains completely revert to their original right-handed alpha-helical form. Successive annealing and solvent treatment steps show that this helix sense inversion cycle can be repeated many times.

Screw-sense inversion characteristic of ?-helical poly(?-p-chlorobenzylL-aspartate) and comparison with other related polyaspartates

This is one of a series of studies on the reversal of the helix sense of polyaspartates originated from the pioneering work of Goodman and his associates in 1960s. Poly(beta-p-chlorobenzyl L-aspartate) (PClBLA) is one of the well-studied polyaspartate derivatives in both solution and the solid state. The chemical structure of PClBLA differs from those of poly(beta-benzyl L-aspartate) (PBLA) and poly(beta-phenethyl L-aspartate) (PPLA) only at the terminal of the relatively long side chain. PBLA takes a left-handed form (L) in conventional helicoidal solvents and does not exhibit any screw-sense inversion. In contrast to PBLA, both PClBLA and PPLA form a right-handed helix (R) in chlorinated alkane solvents and exhibits a reversal of alpha-helix sense at higher temperatures. Yet the transition behaviors in the presence of denaturant acid are quite different between these two polymers. While PPLA exhibits transitions such as R --> L --> coil by lowering temperature, PClBLA directly goes into the coil state without showing the reentrant L form. The cause of these phenomenological differences among these polymers has been investigated by constructing the phase diagram.

Effect of side chain-backbone electrostatic interactions on the stability of alpha-helices

An apparent discrepancy between the observed stability of the C-peptide alpha-helix of ribonuclease A and that computed from the Zimm-Bragg parameters sigma and s (obtained by the host-guest technique) is resolved. Side chain-backbone ion-dipole interactions play a role in both systems. However, they are averaged out in the random copolymers used to determine sigma and s for charged residues such as glutamic acid but not in the specific-sequence copolymer, namely, the C-peptide, where they contribute significantly to the helix stability. In considering a specific-sequence alpha-helix, its intrinsic stabilizing free energy (expressed in terms of sigma and s) must be augmented by position-dependent stabilizing long-range electrostatic interactions.