External chirality-triggered helicity control promoted by introducing a beta-Ala residue into the N-terminus of chiral peptides.
The noncovalent chiral domino effect (NCDE), defined as chiral interaction upon an N-terminus of a 3(10)-helical peptide, will provide a unique method for structural control of a peptide helix through the use of external chirality. On the other hand, the NCDE has not been considered to be effective for the helicity control of peptides strongly favoring a one-handed screw sense. We here aim to promote the NCDE on peptide helicity using two types of nonapeptides: H-beta-Ala-Delta(Z)Phe-Aib-Delta(Z)Phe-X-(Delta(Z)Phe-Aib)(2)-OCH(3) [Delta(Z)Phe = alpha,beta-didehydrophenylalanine, Aib = alpha-aminoisobutyric acid], where X as the single chirality is L-leucine (1) or L-phenylalanine (2). NMR, IR, and CD spectroscopy as well as energy calculation revealed that both peptides alone form a right-handed 3(10)-helix. The original CD amplitudes or signs in chloroform, irrespective of a strong screw-sense preference in the central chirality, responded sensitively to external chiral information. Namely added Boc-L-amino acid stabilized the original right-handed helix, while the corresponding d-isomer destabilized it or transformed it into a left-handed helix. These peptides were also shown to bind more favorably to an L-isomer from the racemate. Although similar helicity control was observed for analogous nonapeptides bearing an N-terminal Aib residue (Inai, Y.; et al. Biomacromolecules 2003, 4, 122), the present findings demonstrate that the N-terminal replacement by the beta-Ala residue significantly improves the previous NCDE to achieve more effective control of helicity. Semiempirical molecular orbital calculations on complexation of peptide 2 with Boc-(L or D)-Pro-OH reasonably explained the unique conformational change induced by external chirality.
Inai
Yoshihito
Y
Department of Environmental Technology and Urban Planning, Shikumi College, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan. inai.yoshito@nitech.ac.jp
Komori
Hisatoshi
H
D002942:Circular Dichroism / Q000379:methods; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared / Q000379:methods; D013237:Stereoisomerism; D015091:beta-Alanine / Q000737:chemistry*
D010455:Peptides; D015091:beta-Alanine