Switching of turn conformation in an aspartate anion peptide fragment by NH · · · O− hydrogen bonds
✍ Scribed by Akira Onoda; Hitoshi Yamamoto; Yusuke Yamada; Keonil Lee; Seiji Adachi; Taka-aki Okamura; Kumiko Yoshizawa-Kumagaye; Kiichiro Nakajima; Toru Kawakami; Saburo Aimoto; Norikazu Ueyama
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2005
- Tongue
- English
- Weight
- 412 KB
- Volume
- 80
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
Aspartic acid protease model peptides Z–Phe–Asp(COOH)–Thr–Gly–Ser–Ala–NHCy (1) and AdCO–Asp(COOH)–Val–Gly–NHBzl (3), and their aspartate anions (NEt~4~)[Z–Phe–Asp(COO^−^)–Thr–Gly–Ser–Ala–NHCy] (2) and (NEt~4~)[AdCO–Asp(COO^−^)–Val–Gly–NHBzl] (4), having an invariant primary sequence of the Asp–X(Thr,Ser)—Gly fragment, were synthesized and characterized by ^1^H‐NMR, CD, and infrared (IR) spectroscopies. NMR structure analyses indicate that the Asp O^δ^ atoms of the aspartate peptide 2 are intramolecularly hydrogen‐bonded with Gly, Ser, Ala NH, and Ser OH, supporting the rigid β‐turn‐like conformation in acetonitrile solution. The tripeptide in the aspartic acid 3 forms an inverse γ‐turn structure, which is converted to a β‐turn‐like conformation because of the formation of the intramolecular NH · · · O^−^ hydrogen bonds with the Asp O^δ^ in 4. Such a conformational change is not detected between dipeptides AdCO–Asp(COOH)–Va–NHAd (5) and (NEt~4~)[AdCO–Asp(COO^−^)–Val–NHAd] (6). The pK~a~ value of side‐chain carboxylic acid (5.0) for 3 exhibits a lower shift (0.3 unit) from that of 5 in aqueous polyethyleneglycol lauryl ether micellar solution. NMR structure analyses for 3 in an aqueous micellar solution indicate that the preorganized turn structure, which readily forms the NH · · · O^−^ hydrogen bonds, lowers the pK~a~ value and that resulting hydrogen bonds stabilize the rigid conformation in the aspartate anion state. We found that the formation of the NH · · · O^−^ hydrogen bonds involved in the hairpin turn is correlated with the protonation and deprotonation state of the Asp side chain in the conserved amino acid fragments. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2005