title: Stabilization of a C7 equatorial gamma turn in DMSO-d6 by a ditryptophan crosslink.
abstract: Covalent crosslinks can control local peptide conformation. In tripeptide sequences of the general formula Cys-Xxx-Cys, cysteine disulfides have been previously shown to enforce a C7 equatorial gamma-turn conformation (also referred to as an inverse gamma-turn). Much less is known about the effects of dityrosine and ditryptophan crosslinks on local peptide structure. In a series of tripeptides, ditryptophan crosslinks were formed using the two-step process of acid-promoted Mannich dimerization followed by oxidative aromatization. In these peptides, with the general formula Trp-Xxx-Trp (Xxx not equal to Gly), ditryptophan crosslinks were found to stabilize a C7 equatorial gamma-turn conformation in DMSO-d6. Rigorous support for a C7 equatorial conformation in the crosslinked sequence Trp-Pro-Trp came from a variety of 1H NMR experiments and molecular modelling. Interproton distances were derived from NOE buildups that were determined through a series of double pulsed field gradient spin echo (DPFGSE) experiments. In addition, the small temperature dependence of the i+2 NH chemical shifts (delta delta/delta T < 2 ppm/degree C) provided further support for the intramolecular hydrogen bond which defines a gamma-turn.
authors.affiliation: Department of Chemistry, University of California-Irvine 92697-2025, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Stachel
authors.forename: H
authors.initials: H
authors.lastname: Hu
authors.forename: Q N
authors.initials: QN
authors.lastname: Van
authors.forename: A J
authors.initials: AJ
authors.lastname: Shaka
authors.forename: D L
authors.initials: DL
authors.lastname: Van Vranken
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry*; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D008958:Models, Molecular; D013057:Spectrum Analysis; D013696:Temperature; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D003432:Cross-Linking Reagents; D004151:Dipeptides; D014364:Tryptophan; D004121:Dimethyl Sulfoxide