Engineering a beta-helical D,L-peptide for folding in polar media.
Beta helices--helices formed by alternating D,L-peptides and stabilized by beta-sheet hydrogen bonding--are found naturally in only a handful of highly hydrophobic peptides. This paper explores the scope of beta-helical structure by presenting the first design and biophysical characterization of a hydrophilic D,L-peptide, 1, that forms a beta helix in methanol. The design of 1 is based on the beta-hairpin/beta helix--a new supersecondary that had been characterized previously only for hydrophobic peptides in nonpolar solvents. Incorporating polar residues in 1 provided solubility in methanol, in which the peptide adopts the expected beta-hairpin/beta-helical structure, as evidenced by CD, analytical ultracentrifugation (AUC), NMR spectroscopy, and NMR-based structure calculations. Upon titration with water (at constant peptide concentration), the structure in methanol (1 m) transitions cooperatively to an extended conformation (1 w) resembling a cyclic beta-hairpin; observation of an isodichroic point in the solvent-dependent CD spectra indicates that this transition is a two-state process. In contrast, neither 1 m nor 1 w show cooperative thermal melting; instead, their structures appear intact at temperatures as high as 65 degrees C; this observation suggests that steric constraint is dominant in stabilizing these structures. Finally, the (1)H NMR C alphaH spectroscopic resonances of 1 m are downfield-shifted with respect to random-coil values, a hitherto unreported property for beta helices that appears to be a general feature of these structures. These results show for the first time that an appropriately designed beta-helical peptide can fold stably in a polar solvent; furthermore, the structural and spectroscopic data reported should prove useful in the future design and characterization of water-soluble beta helices.
Kulp
John L
JL
Division of Chemistry, Naval Research Laboratory, Washington, DC 20375-5342, USA.
Clark
Thomas D
TD
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D015195:Drug Design; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012997:Solvents / Q000737:chemistry; D013696:Temperature
D010455:Peptides; D012997:Solvents