[Leu2]Gramicidin S preserves the structural properties of its parent peptide and forms helically aligned β‐sheets. Issue 10 (6th September 2019)

• Record Type: Journal Article
• Authors: Asano, Akiko; Matsuoka, Shiori; Minami, Chisato; Kato, Takuma; Doi, Mitsinobu
• Is Part Of: Acta crystallographica. Volume 75:Issue 10(2019)
• Page Start: 1336
• Page End: 1343
• Publication Date: 2019-09-06
• Subjects: cyclic decapeptide -- amphiphilicity -- type II' β‐turn -- crystal structure -- chemical shift perturbation; Crystallography -- Periodicals; Crystals -- Periodicals; 548.3
• DOI: 10.1107/S2053229619011872
• Languages: English
• ISSNs: 2053-2296

Abstract

Abstract : [Leu]Gramicidin S could be a novel scaffold for studying β‐turn and sheet structures. Abstract : For crystallographic analysis, Leu was substituted for Orn in Gramicidin S (LGS) to suppress interactions with hydrophilic solvent molecules, which increased the flexibility of the Orn side chains, leading to disorder within the crystals. The asymmetric unit (C62 H94 N10 O10 ·1.296C3 H8 O·1.403H2 O) contains three LGS molecules ( A, B and C ) forming β‐turn and intramolecular β‐sheet structures. With the exception of one motif in molecule C, d ‐Phe‐Pro turn motifs (Phe is phenylalanine and Pro is proline) were classed as type II′ β‐turns. The peptide backbones twist slightly to the right along the long axis of the molecule. The puckering of Pro is in a Cγ‐ endo or twisted Cγ‐ endo –Cβ‐ exo form. Flanking molecules are arranged such that the angles ( A…B = 104°, B…C = 139° and C…A = 117°) form helical β‐sheets. Solvent molecules interact with the peptide backbones supporting the β‐sheets. The forms of the replacement Leu side chains are consistent with the e‐form of the Orn side chain in GS analogues. No hydrophilic region composed of solvent molecules, such as that observed in Gramicidin S hydrochloride (GS·HCl) crystals, was found. The perturbation of αH chemical shifts and coupling constants of CONH showed that the structural properties of GS·HCl and LGS are similar to each other in solution. CD spectra also supported the structural similarity. With the sequence cyclo(–Val–Leu–Leu–d ‐Phe–Pro–)2 (Val is valine and Leu is leucine), LGS lacks the amphiphilicity and antimicrobial activity of parental Gramicidin S (GS). However, the structure of LGS reflects the structural characteristics of GS and no disordering inconvenient for structural analysis was found. Thus, LGS could be a novel scaffold useful for studying β‐turn and sheet structures.